A Pd/Al2O3 monolith catalyst was prepared by wet impregnation. Its excellent performance was demonstrated in the removal of lean methane. After 1000 h of operation, a higher catalytic activity can be sustained. On this basis, a pilot-scale catalytic flow reversal reactor (CFRR) coupled with a central heat exchanger was designed for catalytic removal of ventilation air methane. Experiments showed high methane destruction ratios were achieved at elevated reactor temperatures maintained by reverse flow operations. Transient and steady characteristics of the reactor were also studied experimentally and analyzed under various operating parameters involving methane concentration, cycle period, and heat transfer flux. The coupling of central heat exchanger caused the complex quasi-periodic states and the significant divergences on the reactor behaviors compared with the results in the literature. To further verify the robustness of the heat recovery method, the experimental unit was operated in a long-time course. The lean methane can be efficiently eliminated and utilized.

•Uniform [Ni3(HCOO)6] frameworks were prepared without additional solvent.•The frameworks preferably adsorb CH4 over N2 superior than most of conventional adsorbents.•PSA experiments showed that both CH4 purity and recovery could exceeded 90%.Adsorption-based separation of CH4/N2 mixture remains challenging. To this end, [Ni3(HCOO)6] frameworks were synthesized by a novel solvent-free method and used as adsorbent. CH4 and N2 adsorption performances of the samples were examined separately by static adsorption, breakthrough and two-bed pressure swing adsorption (PSA) experiments. CH4 adsorption capacity was 0.82 mmol/g at 298 K and 100 kPa. The CH4/N2 selectivity reached up to 6–7 at 298 K and 0.5 MPa, which was higher than that of most other adsorbents including activated carbon, zeolites, and metal-organic frameworks (MOFs). Two-bed lab-scale PSA experiments dealing with equimolar CH4/N2 mixture showed that both CH4 purity and recovery exceeded 90% under optimized operation conditions. The remarkable performance in benchmarking experiments confirmed [Ni3(HCOO)6] frameworks promising adsorbent for unconventional natural gas upgrading, owing to its high volume of uniform ultra-micropore and optimal polarizability.Download high-res image (165KB)Download full-size image

In this work, we show a solvent-free “explosive” synthesis (SFES) method for the ultrafast and low-cost synthesis of metal-formate frameworks (MFFs). A combination of experiments and in-depth molecular modelling analysis – using grand canonical Monte Carlo (GCMC) simulations – of the adsorption performance of the synthesized nickel-formate framework (Ni-FA) revealed extremely high quality products with permanent porosity, prominent CH4/N2 selectivity (ca. 6.0), and good CH4 adsorption capacity (ca. 0.80 mmol g−1 or 33.97 cm3 cm−3) at 1 bar and 298 K. This performance is superior to those of many other state-of-the-art porous materials.

•The catalytic oxidation performance has been promoted after this treatment.•The etched catalysts maintain excellent thermal resistance.•Citric acid works as an etching agent because of its moderate reducing capacity.•The specific surface area has been increased because of the improvement of porosity.This work concentrates on the improvement of LaMnO3 perovskite catalysts for methane combustion by an effective and mild citric acid etching strategy. The etched catalysts showed improved catalytic activity due to higher surface area, abundant vacancies, higher surface Mn4 +/Mn3 + ratio and more active oxygen species. Furthermore, the pre-treated catalysts maintained good stability because of the maintenance of perovskite structure.

Metal–organic frameworks (MOFs), assembled by metal ions or their clusters and organic linkers, are one of the state-of-the-art crystalline materials. Their features such as ultra-high porosity, synthetic tailorability and relative ease of synthesis make them promising candidates for diversified applications. Controllable integration of MOFs and carbon-based materials not only leads to further enhancement of single-phase MOFs in terms of stability and electrical conductivity, but also surprisingly brings about a number of new functionalities like formation of new pores and template effects. These benefits allow the resultant MOF–carbon composites to be applied beyond the fields of single-phase MOFs. Increasing research interests have been aroused in this rapidly developing interdisciplinary area. This review aims to specifically group together the important reports focused on MOF–carbon composites till now. The methods used for composite synthesis and applications of the composites are investigated and categorized. The review also exclusively discusses the functionalities stemming from the synergistic effects of the two intriguing materials and pictures the future prospects at the end.

•A series of isostructural ultra-microporous MOFs are readily synthesized.•The pore size and internal surface properties are tuned by using different metal ions.•The adsorption behaviour of gas molecule in [M3(HCOO)6] is revealed by NH3-TPD.A series of isostructural ultra-microporous metal-organic framework (MOF) compounds [M3(HCOO)6] (M = Mg, Mn, Co and Ni) have been readily synthesized in large-scale, characterized, and evaluated for the separation of CH4 and N2. Results indicate that the metallic formates exhibit different CH4 adsorption capacities and distinct CH4/N2 selectivity in a sequence of Ni > Co > Mg > Mn analogue owing to their varied CH4 affinities. Thereinto, [Ni3(HCOO)6] shows the highest CH4 adsorption capacity of 1.09 mmol/g and CH4/N2 selectivity up to 6.5 at 0.4 MPa and 298 K in the dynamic experiments, which suggests the most suitable synergistic effect between constricted pores and surface properties among [M3(HCOO)6] frameworks. At the same time, the adsorption behaviour in [M3(HCOO)6] is investigated by NH3-TPD, revealing that the adsorbed NH3 molecules should have two different states. One is that gas molecules stay inside the pores, the other is that gas molecules are adsorbed on the adsorption sites induced by the coordinated metal ions or exposed oxygen of the [M3(HCOO)6], which directly affects the adsorption capacity, the ratio of two states of molecules and the final selectivity. These results confirm that alteration of metal ion plays an important role in the tuning of pore size and internal surface properties, thus providing new clues to design MOFs with different pore characteristics for enhanced gas sorption and separation.

•The uniform [Mg3(OOCH)6] crystals were synthesized with the modulation of HF.•By varying the amount of HF different crystals size and morphology were obtained.•The Mg2+-induced sites and ultra-micropore can effect the selectivity of CH4/N2.Ultra-microporous [Mg3(OOCH)6] frameworks with different uniform shapes, were synthesized via a facile coordination modulation method, in which HF was used as a modulator to promote the growth of [Mg3(OOCH)6] crystals. The as-prepared [Mg3(OOCH)6] frameworks were scrutinized and evaluated the CH4 adsorption capacity and selectivity over N2 by pure gas adsorption and breakthrough experiments. The [Mg3(OOCH)6] frameworks exhibit preferential adsorption of CH4 over N2, and much higher CH4 adsorption capacity (up to 0.74 mmol/g) by comparison with conventional zeolites. It has been confirmed that the equilibrium selectivities of [Mg3(OOCH)6] frameworks are shape dependent, and the uniform prism-like framework with size of 100 μm has the highest selectivity up to 5.5 at 298 K. These results suggest that achieving the optimal coupling of polarizability and structure of [Mg3(OOCH)6] framework is key factor to obtain a high selectivity for the separation of CH4/N2 mixture.

•An integrated natural gas fuel processor was developed and tested for 2-kW SOFC.•The multilayered cylindrical structure reformer was suitable for hydrogen production.•The relationship between the structure, temperatures and efficiency was investigated.•74.11% of the energy efficiency of the integrated fuel processor can be reached.•Coupled the fuel processor with a SOFC, the joint-test experiments were performed.A natural gas fuel processor integrated a compact reformer with two heat exchangers was developed and tested as a hydrogen generator for 2 kW distributed solid oxide fuel cell (SOFC) applications. The compact reformer is comprised of a reforming chamber and two non-catalytic combustion chambers, in which the endothermic and exothermic reactions are coupled into a multilayered cylindrical reactor vessel. The integrated fuel processor can be started up quickly by the combustion of methane and run steadily within 30 min under the preferred thermodynamic operating conditions. The higher temperature zone is located at the latter half part of the reforming chamber, where the temperature gradient is relatively small and favorable for hydrogen production. The results show that a high methane conversion and H2 molar fraction (dry basis) can be achieved, irrespective of the hydrogen production capacity. The energy efficiency of the integrated fuel processor can reach 74.11% when producing 2 Nm3/h of H2. A SOFC system was fueled successfully by the generated hydrogen-rich reformate in the integrated fuel processor.For supplying hydrogen to 2-kW SOFC, an integrated fuel processor composed of compact reformer, heat exchangers and other auxiliary equipment was developed and tested, in which methane can be converted into hydrogen-rich reformates.

Catalyst stability is an urgent issue for ethyl-anthraquinone (EAQ) hydrogenation to produce the environment friendly oxidant H2O2. Herein, a highly stable egg-shell Pd/SiO2/cordierite monolith catalyst (PSC) was prepared by an impregnation method. For comparison, a Pd/Al2O3/cordierite monolithic catalyst (PAC) was also prepared. The stability tests of the catalysts were conducted in a continuous trickle bed reactor at 40 °C with a high liquid space velocity of 25 h−1. It turned out that the PSC catalyst obtained a stable H2O2 yield in the 1000 h test while the PAC catalyst deactivated in 100 h. The as-prepared catalysts were characterized by X-ray diffraction (XRD), N2 adsorption, NH3 temperature programmed desorption (NH3-TPD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). N2 adsorption and NH3-TPD results showed that the PSC catalyst had a regular structure and very weak acidity, which contributed to improving the catalyst selectivity and stability. Besides, the lower support calcination temperature was found to be beneficial to improving the hydrogenation efficiency because of higher Pd dispersion and lower Pd loss.

Aluminum suspensions with different properties were prepared and characterized by UV–Vis spectra, BET, XRD and NH3-TPD. A layer of Al2O3 was coated onto the cordierite monolith by sol–gel method. Pd/Al2O3/cordierite monolith catalysts with the same Pd loading and particle size were prepared, and tested by nitrobenzene hydrogenation under solvent-free conditions. The adsorption of nitrobenzene on acid sites might be the primary effect under the reaction conditions, and a good linear relationship between hydrogenation rate and the acid content of the Al2O3 layer was observed. Furthermore, the stronger acid sites were responsible for the lower aniline selectivity.

The effects of Fe promotion were investigated on the activity and selectivity of Rh/CeO2 catalyst for the direct synthesis of ethanol from syngas. The catalysts were comprehensively characterized by X-ray diffraction (XRD), N2 adsorption–desorption, CO uptake, H2-TPR, temperature programmed surface reaction (TPSR), and FT-IR. XRD, CO uptake and FT-IR measurements indicated that Rh particles were well dispersed. TPSR results revealed that the addition of Fe changed CO dissociation behavior over the catalysts. FT-IR results showed that Fe promoter stabilized both linear carbonyl and gem-dicarbonyl species, which could be responsible for the improved catalytic activity. The interaction between Rh and Fe species is proposed to play a crucial role in achieving higher ethanol selectivity.

Silica nanoparticles with different sizes (ranging from 10 nm to 104 nm) and size distributions were synthesized by semi-batch and semi-batch/batch methods of the Stöber process. Then the amorphous silica with different surface areas (ranging from 30m2/g to 400m2/g) and pores (ranging from 3 nm to 33 nm) were obtained by various aging treatments and drying methods of the synthesized colloidal silica sol. The aging treatment resulted in the monodispersed pore distribution and decreased BET surface area of silica. The high-humidity drying method led to the mesoporous silica with uniform pores and decreased small pores. As the silica was obtained by the arrangement of silica nanoparticles, the pore diameter and pore distribution of mesoporous silica were directly related to the size and distribution of nanoparticles. Furthermore, this study offered a new thought for the synthesis of other mesoporous materials with uniform pore distributions.

CO2 adsorption and methanation on a Ni/Ce0.5Zr0.5O2 catalyst has been investigated using in situ FTIR spectroscopy. CO2 adsorption and methanation experiments were conducted on both components of the support and the catalyst to identify the adsorption species and any intermediate species. It was proposed that CO2 prefers to adsorb on surface oxygen sites adjacent to Ce(III) compared with those adjacent to Ce(IV)/Zr or surface hydroxyl sites. Five adsorption species were revealed for CO2 adsorption on Ni/Ce0.5Zr0.5O2 and monodentate carbonates formed on Ce(III) are easier to be hydrogenated than those on Ce(IV). Formate species were found to be the main intermediate species during the reaction and Ce(III) sites were proposed to be active sites for their hydrogenation. The adsorption and hydrogenation of formic acid were also conducted to confirm the identification of the intermediate species during the reaction. –CH2OH species were detected for the first time and found to be the further intermediates in the reaction.

A series of nickel catalysts supported on Ce0.5Zr0.5O2 were prepared by impregnation (IMP), deposition–precipitation (DP) and urea combustion (UC) methods. Their performances of CO2 methanation were investigated for the production of synthetic natural gas from coal. The catalysts were characterized by BET, H2-chemisorption, XRD, Raman, XPS, CO2-TPD and H2-TPR techniques. The results indicated that Ni/Ce0.5Zr0.5O2 catalysts prepared by impregnation method showed the highest activity. It can attain 73% CO2 conversion at 300 °C with a reaction rate of 20.5 mmol CO2/(gcat min) and have a CH4 selectivity of 100%. The higher activity of IMP sample is due to its higher nickel surface area, oxygen vacancies, Ce(III) and basic sites than others.

•Two ultra-microporous frameworks were synthesized in a feasible route to scale up.•The CH4/N2 separation performances for MOFs and zeolites were evaluated.•The highest selectivities ever reported for the separation of CH4 against N2 were achieved.•The mechanism explains the good separation performances for the two adsorbents.Two typical ultra-microporous adsorbents namely [Ni3(HCOO)6] and [Co3(HCOO)6] were successfully prepared in a feasible route to scale up using non-corrosive methyl methanoate instead of formic acid. Pure gas and binary gas mixture adsorption equilibria of CH4 and N2 were conducted on the two compounds to evaluate their CH4 adsorption capacities and selectivities against N2. The two compounds exhibit preferential adsorption of CH4 over N2 at 298 K in the pressure range 0.1–1.0 MPa, and the adsorption selectivities of CH4/N2 mixture are determined to be 6.0–6.5 for [Ni3(HCOO)6] and 5.1–5.8 for [Co3(HCOO)6], respectively. The uniform ultra-micropores and optimal polarizability resulted from multiple coordination modes play the essential roles in their preferential adsorption of CH4 with the highest selectivities up to date, making the two compounds as promising candidates of existing adsorbents for unconventional natural gas upgrading.

Separation of methane and nitrogen is an important issue in upgrading low-quality natural gas, and non-cryogenic, adsorption-based separation of CH4/N2 is particularly challenging. In this report, a metal–organic framework (MOF) adsorbent, namely a [Ni3(HCOO)6] framework, is comprehensively investigated for the separation of CH4–N2 mixture via pure gas adsorption and binary gas breakthrough experiments. All the prepared samples synthesized using different routes were also studied in detail by powder XRD, FT-IR, SEM, TGA/DSC and argon adsorption. The results show that the adsorptive separation performances can be improved significantly by optimizing the synthesis of the framework. The precursors play crucial roles in the crystallization of [Ni3(HCOO)6] frameworks, giving rise to a variability in ultra-micropore volume, surface area and pore size. Good crystallization can result in large ultra-micropore volume and furthermore brings about high separation selectivity. The [Ni3(HCOO)6] framework synthesized from nickel nitrate and methyl formate exhibits the best crystallization and the largest micropore volume, leading to the highest CH4/N2 separation selectivity of up to 7.5 in the pressure range of 2.0–10 bar, which is the highest value reported for MOFs. Moreover, this adsorbent presents uniform nanosized crystals (∼140 nm), permanent porosity and consistent separation performances, making the [Ni3(HCOO)6] framework a promising candidate for natural gas upgrading.

The effects of Ce-ZrOx, Ce-LaOx, Ce-SmOx and Ce-GdOx additions to Rh/Al2O3 catalysts on methane autothermal re-forming were investigated. Activity tests showed that the addition of Ce-ZrOx could significantly reduce the concentration of CO in reformats. When Ce/Zr atomic ratio was 1:1, Ce0.5Zr0.5O2 solid solution with high thermal stability was obtained, which could effectively improve the catalytic performance effectively. The additives of alkaline-earth metals (Mg, K and Ca) on the catalytic properties were also studied. The results of experiments showed that the addition of MgO to Rh/Ce0.5Zr0.5O2/Al2O3 improved the stable performance and the carbon resistance of the catalyst. The optimized catalyst was 0.1%Rh/2.0%MgO/40%Ce0.5Zr0.5O2/Al2O3, which showed a highly stable performance for methane autothermal reforming.TPR profile of a series of methane ATR catalysts

The mesostructured Al-BDC metal–organic frameworks (MOFs) with an average pore size of 2.58 nm were prepared via a simplified washing and drying process and applied to the separation of CO2/CH4 mixtures. The adsorption equilibrium and thermodynamics of CH4 and CO2 were studied in the dynamic processes by the volumetric–chromatographic and inverse gas chromatographic (IGC) methods. The experiments represent that the Al-BDC MOF with large pore size has a much higher CO2/CH4 selectivity of ca. 24 at 303 K in the pressure range 0–1.0 MPa and therefore appears to be a good candidate for the separation of CH4 from CO2. The initial heats of adsorption of CH4 and CO2 on the mesostructured Al-BDC MOFs were determined to be 11.5 and 25.2 kJ mol–1 by the IGC method, respectively, which are significantly reduced by ca. 25% compared with that on the microporous Al-BDC MOFs. The results indicate that the expanded pore size not only greatly increases the selectivity of CO2 adsorption over CH4 but also reduces the adsorption heat, revealing that it should be the desired method to obtain a satisfactory absorbent for CO2/CH4 separation.

Carbon deposition over a Ni/Al2O3 methanation catalyst was studied emphasizing the effects of operating conditions. A method to quantify the deposited carbon was developed from TG analysis, and samples were also characterized by TPO and TEM. Carbon formation boundaries were presented in a CHO ternary diagram based on thermodynamic calculations. In the carbon-forming region, it is found that both the temperature and H2/CO ratio are significantly influential factors for the morphology and amount of carbon deposits. The amount of generated carbon varies with reaction time nonlinearly, meanwhile carbon laydown is favored by low pressure and space velocity. Consequently, it provides guidance for the optimization of operating conditions.

The sintering behavior of a co-precipitated Ni/Al2O3 methanation catalyst is studied by investigating the effect of treating time, temperature and atmosphere. Fresh and sintered samples are characterized by N2 physisorption, H2 chemisorption, temperature programmed reduction, X-ray diffraction and transmission electron microscopy. A reduction both in total and nickel surface area has been observed, the extent depending on the experimental conditions. Sintering of the studied catalyst, reflected by a significant decrease of nickel surface area, is a combined effect of primary encapsulation of metallic nickel due to the collapse of the support structure and sporadic agglomeration of nickel crystallites. The formation of a Ni2+ doped alumina phase, induced by steam ambience, further accelerates loss of surface nickel atoms. It is found that the sintering rate obeys a simple power law expression, with the apparent activation energy value of 118 kJ/mol. The sintered methanation catalyst suffers considerable decay of CO hydrogenation activity in a simulated industrial atmosphere, which suggests that extraordinarily high temperatures should be avoided as much as possible in the practical operation.

Pd/Al2O3 catalysts modified by different metal oxides (Mn, Fe, La, Mg and Ni oxides) were prepared and tested for fuel-lean methane/air catalytic combustion. It was found that the support material influenced the combustion performance significantly. The addition of NiO or MgO effectively improved the activity and hydrothermal stability of catalysts. X-ray diffraction (XRD) results showed the presence of spinel phase in the Pd/Al2O3–NiO and Pd/Al2O3–MgO catalysts. Temperature-programmed desorption of ammonia (NH3-TPD) measurements indicated that the supports became weakly acidic because of the formation of NiAl2O4 or MgAl2O4 spinel. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed the well dispersion of Pd particles on the Al2O3–NiO and Al2O3–MgO supports. It was concluded that the formation of the NiAl2O4 or MgAl2O4 spinel phase during preparation would be beneficial for the methane catalytic performance of Pd catalysts.Highlights► Catalysts for methane combustion under lean-burn conditions ► Addition of Ni or Mg oxide improves the catalytic performance of Pd/Al2O3. ► Aluminate spinels are formed after adding Ni or Mg oxide to the supports. ► Aluminate spinels weaken the acidity of support and prevent oxidation of Pd. ► Support with spinel phase stabilizes Pd against aggregation during reaction.

The Cu-based catalysts with different supports (CeO2, ZrO2 and CeO2–ZrO2) for methanol steam reforming (MSR) were prepared by a co-precipitation procedure, and the effect of different supports was investigated. The catalysts were characterized by means of N2 adsorption–desorption, X-ray diffraction, temperature-programmed reduction, oxygen storage capacity and N2O titration. The results showed that the Cu dispersion, reducibility of catalysts and oxygen storage capacity evidently influenced the catalytic activity and CO selectivity. The introduction of ZrO2 into the catalyst improved the Cu dispersion and catalyst reducibility, while the addition of CeO2 mainly increased oxygen storage capacity. It was noticed that the CeO2–ZrO2-containing catalyst showed the best performance with lower CO concentration, which was due to the high Cu dispersion and well oxygen storage capacity. Further investigation illuminated that the formation of CO on CuO/ZnO/CeO2–ZrO2 catalyst mainly due to the reverse water gas shift. In addition, the CuO/ZnO/CeO2–ZrO2 catalyst also had excellent reforming performance with no deactivation during 360 h run time and was used successfully in a mini reformer. The maximum hydrogen production rate in the mini reformer reached to 162.8 dm3/h, which can produce 160–270 W electric energy power by different kinds of fuel cells.Highlights► Correlation between catalyst structure and performance for methanol steam reforming. ► Effect of CeO2–ZrO2 carrier on the catalytic performance. ► Route of CO formation and mechanism of MSR on the CuZnCeZr catalyst. ► CuZnCeZr catalyst showed good stability during the 360 h stability test. ► CuZnCeZr catalyst performance in mini reformer.

Based on computational fluid dynamics (CFD), gas−liquid mass transfer in upward Taylor flow through vertical circular capillaries was studied. To save computational resources and time, the numerical simulations were carried out in a moving frame of reference attached to Taylor bubbles. Three consecutive Taylor bubbles were used to mimic the behavior of Taylor flow in an infinitely long capillary. Steady-state solutions of concentration fields were obtained to describe gas transfer from Taylor bubbles to the liquid phase. The liquid-phase volumetric mass-transfer coefficient, KLa, was investigated as a function of various parameters, including the liquid-film length, liquid-slug length, liquid-film thickness, bubble rise velocity, liquid-phase diffusivity, capillary diameter, and gravity. One fitted equation, expressed with three dimensionless numbers, was developed to quantify the relationship between KLa and the above parameters. The examples show that the equation could predict KLa well. The contributions of the cylindrical bodies and hemispherical caps of Taylor bubbles on the overall mass transfer were studied separately.

A compact methanol reformer for hydrogen production has been successfully fabricated, which integrated one reforming chamber, one water gas shift reaction chamber, two preheating chambers and two combustion chambers. It can be started-up at room temperature by the combustion of liquid methanol in the combustion chamber within 7 min without any external heating. The cold start response of the methanol reformer has been investigated using different parameters including methanol and air supply rate, and the experiments revealed that the optimum methanol and air flow rate were 0.55 mL/min and 3 L/min respectively. The results indicated that this methanol reformer can provide a high concentration of hydrogen (more than 73%) and the system efficiency is always maintained above 74%. It is further demonstrated in more than 1600 h continuous performance that the reformer could be operated autothermally and exhibited good test stability.

Autothermal reforming of methane (ATR) was studied over Rh catalysts supported on Ce0.5Zr0.5O2 solid solution, which were synthesized by four different routes, including reverse micro-emulsion (ME), co-precipitation (CP), urea-combustion (UC) and sol–gel (SG) method. The textural and structural properties of the as-prepared solid solutions were carefully examined by means of BET, TEM, XRD and Raman techniques. Results showed that the ME sample exhibited a single cubic phase, whereas tetragonal or mixed phases such as cubic CeO2-rich and tetragonal ZrO2-rich phases, were found in the case of CP, UC and SG. Vegard's rule revealed that the homogeneity of these as-prepared solid solutions followed the order of ME > CP > UC > SG. TPR and CO-pulse experiments were adopted to evaluate the reducibility and the oxygen storage capacity (OSC) of the catalysts. It was found that the more homogenous the solid solution is, the more reducibility it is, i.e. both the reducibility and OSC followed the same order as that of homogeneity.Rh/ME showed the highest activity and H2/CO ratio and such performance was maintained without significant loss during 10 h experiment. On the contrary, the other three catalysts having mixed phases showed remarkably deactivation in terms of H2/CO due to the loss of BET area. To elucidate the resistance toward carbon formation of these catalysts, methane decomposition experiments and following temperature-programmed-oxidation (TPO) were studied. As expected, the resistance toward carbon formation could be enhanced by the improved OSC of the catalyst.

The characteristics of the pressure drop of fluid were investigated in three different kinds of stainless steel microchannels with diameter of 0.56, 1.00, and 1.80 mm based on the absorption in the microchannels. For the single-phase flow pressure drop, nitrogen being used as the test fluid, it was found that the transition between the laminar and turbulent flow occurred at the Reynolds number of about 2000, which was different from some previous reports in which the early flow transition was observed in microchannels. For the two-phase flow pressure drop, an industrial chemical absorbent (40 wt % MDEA solution) and nitrogen being taken as the working fluid, it was found that the existing correlations including the homogeneous flow model and separated flow model failed to predict the experimental results because of the special operating condition in which the ratio of volumetric flow rate of gas to liquid phase ranged from 100 to 3400. A new correlation to predict the two-phase flow pressure drop was developed in the form of the Lockhart−Martinelli type which considered the effect of surface tension, gas phase inertial force, Reynolds number of liquid phase, and the Martinelli parameter. The predicted data with new correlation showed good agreement with the experimental results.

Flow pattern, pressure drop, and mass transfer characteristics have been studied for the gas−liquid two-phase flow in a 1.0 mm inner diameter circular microchannel reactor. A mixture of CO2, N2, and polyethylene glycol dimethyl ether was used to represent the gas and liquid phases, respectively. Bubbly, slug, churn, and slug-annular flow patterns were observed in the present work. A flow pattern map using superficial gas and liquid velocities as coordinates has been developed and compared to the existing flow pattern maps for ∼1 mm diameter channels. The data obtained for the pressure drop of the two-phase flow were analyzed and compared with the homogeneous model and the separate flow model to assess their predictive capabilities. The liquid side volumetric mass transfer coefficient increased with an increase of the superficial gas and liquid velocities, and the influences of the superficial gas and liquid velocities on it were demonstrated. The liquid side mass transfer coefficient, which was as high as 3.34 s−1, was 1 or 2 orders of magnitude higher than the traditional industrial gas−liquid contactors.

This study provides experimental data on the performance of microchannel contactors for CO2 absorption. An aqueous solution of piperazine (PZ) activated N-methyldiethanolamine (MDEA) and a mixture of CO2/N2 were selected as the working fluids. Three different sizes of microchannels, with hydraulic diameters of 0.5, 1, and 2 mm and the same length of 180 mm, served as the contactors. With a decrease in the hydraulic diameter the larger surface to volume ratio can be achieved. The mass transfer rates increased considerably, and the size effect of mass transfer was observed. Various operating parameters, including the activator, the temperature of gas and liquid flow, the inlet CO2 molar fraction, the superficial gas and liquid velocities, and the operating pressure were also evaluated. The results obtained illustrated a great potential of microchannel contactors when they were applied to the separation of CO2.

Monolithic catalysts, Ru/Al2O3–ZrO2/cordierite, were prepared by dipcoating and impregnation for liquid-phase selective hydrogenation of benzene to cyclohexene in a continuous fixed bed reactor. Ru/Al2O3–ZrO2/cordierite showed excellent catalytic performance due to the high specific surface area and the large pores of Al2O3–ZrO2 support. The Zr/Al ratio was optimized to be 0.116 and the excessive amount of ZrO2 resulted in a decreased specific surface area of the Al2O3–ZrO2 washcoating layer. The preferable calcination temperature is 1373 K for Al2O3–ZrO2 support, at which suitable BET surface area and pore size distribution could be obtained. It was also found that appropriate ratio of Zn/Ru was essential to obtain high selectivity. Additionally, compared to the powder catalysts used in the slurry reactor, the monolithic catalysts exhibited much higher activity regarding the yield of cyclohexene and cyclohexane.Ru/Al2O3–ZrO2/cordierite monolithic catalysts were found to be an efficient catalyst for liquid-phase selective hydrogenation of benzene to cyclohexene in a fix-bed reactor. High cyclohexene yield was achieved on the catalyst, due to its high content of large pores in the coating layer, where the consecutive hydrogenation of cyclohexene to cyclohexane was readily prohibited.

Autothermal reforming of methane was studied over La-doped ceria–zirconia-supported Rh catalysts. The CH4 conversion increased from 49 to 60% on increasing the content of La3+ from 5 to 15%, while further increase in the La3+ content led to a slight decrease on both CH4 conversion and H2 selectivity. H2-TPR and UV–vis DRS spectrum showed that the interaction between Rh and the support was enhanced by increasing the content of La. We speculated that a so-called “Rh–La interfacial species” was formed on the surface of the support, which played an important role in catalytic activity. The balance between exposed Rh and the “Rh–La interfacial species” was necessary to improve the catalytic activity. Upon increasing the Rh loading on 15% La-doped ceria–zirconia support, the balance was built, i.e., CH4 conversion increased from ~60 to 69% by increasing Rh loading from 0.1 to 0.5 wt% and only 2% conversion was elevated by doubling the Rh loading from 0.5 to 1.0 wt%.

A WO3/CeO2-ZrO2 catalyst system was discovered for selective catalytic reduction of NOx with NH3; the catalyst (10 wt% WO3 loading) showed nearly 100% NOx conversion in a temperature range of 200–500 °C, at a space velocity of 90000 h−1 in a simulated diesel exhaust containing 550 ppm NOx (NO : NO2 feed ratio at 1.0), 10 vol% H2O and 10 vol% CO2; the catalyst also exhibited high temperature stability.

Methanol autothermal reforming was thermodynamically analyzed using FLUENT software. The calculation methodology using this software is simple and convenient, and its validity was confirmed by comparing the obtained data with previous studies. As a function of the effects of temperature, pressure, molar steam-to-carbon ratio (S/C), and molar oxygen-to-carbon ratio (O/C) on the objective products, favorable operational parameters were evaluated, under which H2 yield maximizes, the CO molar fraction minimizes and carbon deposition can be eliminated. The equilibrium constants of the possible reactions involved in oxidative methanol steam reforming, coupled with the reaction mechanism for the entire investigated temperature range, were elucidated and discussed. On the basis of the concluded possible mechanisms, three areas are inferred. In each individual area, H2 or CO yield reached a maximum, or solid C was efficiently suppressed. Therein, a favorable operational range is proposed to assure the most optimized product yield.

Highly efficient Cu–Mn spinel catalysts for water gas shift (WGS) reaction were achieved by a single step urea-nitrate combustion method. A series of doped Cu–Mn-M catalysts (M = Ce, Zr, Zn, Fe, Al) were prepared by the same method. Effects of dopants on WGS activity and stability of doped Cu–Mn catalysts were investigated. The doped catalysts were characterized by BET, XRD and TPR. XRD results showed that non-doped samples and Zr-doped samples are mainly composed of Cu1.5Mn1.5O4 phase, while CuO, Cu2O and Cu1.5Mn1.5O4 for other doped samples. It was further found that WGS activities depend strongly on the natures of the dopant employed despite of their lower content, varying in the order of Zr > Fe > non-doped > Ce > Al > Zn. TPR profiles revealed that all dopants shift the reduction peaks to lower temperature region, indicating no direct correlation between WGS activity and the reducibility. In addition, Zr-doped Cu–Mn catalyst with 5 wt.% content showed the best catalytic performance and, optimal stability exposed to oxygen-stream and on-stream operation. It indicates that ZrO2 is an effective promoter for Cu–Mn catalyst, and the catalytic performances are related to the existence of a Cu1.5Mn1.5O4 phase and ease reducibility of the catalysts.

Autothermal reforming of methanol for hydrogen production was investigated over ZnO–ZnCr2O4 supported on a series of metal oxides (Al2O3, CeO2, ZrO2 and CeO2–ZrO2). CeO2–ZrO2 mixed oxides with Ce /Zr molar ratio of 4/1 was found to be the optimal support which showed significant effect on the catalytic activity and selectivity. The ZnO–ZnCr2O4/CeO2–ZrO2 and ZnO–ZnCr2O4 catalysts were characterized by XRD, TEM, H2-TPR and XPS. The results show that CeO2–ZrO2 mixed oxides have significant effect on the catalytic performance and the supported catalyst shows more uniform temperature distribution in the catalyst bed which was mainly due to its reasonable redox properties.

A series of monolithic catalysts of mixed metal oxides (ZnO–ZnCr2O4/CeO2ZnCr2O4/CeO2–ZrO2ZrO2) for methanol auto-thermal reforming (ATR) has been studied. The CeO2CeO2–ZrO2ZrO2 modified Zn–Cr-oxide catalysts showed high selectivities and stabilities. Characterization by XRD and TPR showed that the Ce/Zr molar ratio was an important factor for the stabilities of the Zn–Cr catalysts due to the redox properties of the CeO2CeO2–ZrO2ZrO2. The optimal molar ratio of Ce to Zr was 41. The addition of the CeO2CeO2–ZrO2ZrO2 mixed oxides decreased the crystallite size of the Zn–Cr oxide. Operation parameters such as the ratios of oxygen to methanol and water to methanol were studied. The ZnOZnO–ZnCr2O4/CeO2ZnCr2O4/CeO2–ZrO2ZrO2 catalyst exhibited very good stability during 1000 h test.

Monolithic catalysts were prepared by washcoating Ce0.8Zr0.2O2 slurries and then impregnating platinum or rhenium onto cordierite substrates, and characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), inductively coupled plasma (ICP), temperature-programmed-reduction (TPR) and temperature-programmed deposition of CO (CO-TPD) techniques. The effects of preparation parameters on the catalytic performance for water gas shift (WGS) reaction were investigated in details, including different Ce0.8Zr0.2O2 powder as washcoat, coat loadings, metal loadings, Pt/Re weight ratio and impregnation sequences. In addition, pyrophoricity (exposure to oxygen stream) and long-term stability were carried out over monolithic catalysts with the optimized composition. The results showed that Ce0.8Zr0.2O2 prepared by microemulsion methods was the preferred washcoat, and that 50 wt% Ce0.8Zr0.2O2 coat loading and 0.68 wt% Pt loading were required to reduce CO content to ca. 1%. The optimal catalytic performance was achieved over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce0.8Zr0.2O2–M/cordierite catalyst. Pyrophoricity tests indicated that no obvious activity loss was observed over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce0.8Zr0.2O2–M/cordierite catalyst after three exposures to oxygen; while 17% of the initial activity was lost over industrial B206 after one exposure. Monolithic 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce0.8Zr0.2O2–M/cordierite catalyst exhibited good stability during 80 h on-stream test.

A Ru/Al2O3/cordierite monolithic catalyst was prepared, characterized, and examined in selective hydrogenation of benzene to cyclohexene in a monolithic fixed-bed reactor with an aqueous solution of ZnSO4. The Carberry number and Wheeler−Weisz group were calculated to analyze the effects of external and internal diffusions of H2, benzene, and cyclohexene. According to the results of calculations, the water film, solubility, and diffusion coefficients of the three reactants (H2, benzene, and cyclohexene) play important roles in the mass-transfer rate. Under proper reaction conditions, the effects of the external mass transfer of H2 and benzene on the reaction rate are negligible. For the hydrogenation of cyclohexene, the diffusion of cyclohexene from the organic phase to the catalyst is the limiting step in the presence of water, which is the most important factor for obtaining high cyclohexene selectivity. The absence of pore diffusion of the three reactants, which is attributed to the thin eggshell distribution of in the catalyst, is another important factor for the higher cyclohexene selectivity. In addition, the optimum reaction conditions were found to be 413−423 K and 5 MPa.

Oxidative steam reforming of methanol (OSRM) reaction was investigated over a novel monolithic ZnO–Cr2O3/CeO2–ZrO2 catalyst developed in our laboratory. A novel flat-bed reactor was designed to measure the concentration profiles of the monolithic catalyst beds under different operation conditions: water-to-methanol mole ratio (W/M) between 1 and 1.5; oxygen-to-methanol mole ratio (O/M) in the range of 0.1–0.3; space velocity ranging from 1840 to 2890 h− 1; and reaction temperature in the scale of 400–440 °C. On the basis of these results, reaction pathways for the OSRM were discussed. It is indicated that only three independent reactions dominate in our reaction system, namely, the partial oxidation of methanol, the steam reforming of methanol and the methanol decomposition reaction, whereas the water–gas shift and the reverse water–gas shift reactions should be ignored. In addition, the steam reforming of methanol proceeds along all the catalyst bed, whereas methanol decomposition and oxidation reactions occur mainly at the entrance of the catalyst bed.

A novel mini-reactor for hydrogen production has been successfully fabricated, which integrates one reforming chamber, one catalytic combustion chamber and two preheating chambers. It can be started up at room temperature by the combustion of liquid methanol in the combustion chamber within 10min, and it also can keep self-sustained, i.e. without any external heating during the operating process.This reactor has been tested for carrying out the reaction of autothermal reforming of methanol for hydrogen production. The reactor performance has been investigated using three crucial parameters, namely, the molar ratios of water/methanol, oxygen/methanol and the flow distribution, respectively. The experimental runs have demonstrated the optimal methanol conversion of 96.4%, containing 51.04% H22, 26.68% N22, 2.12% CO and 20.16% CO22 in the reformed gas.Furthermore, the reformer which can supply reformed gas at the maximum flow rate of 125 l (STP)/h has been integrated with a miniature fuel cell, the small power system can produce continuous power at the energy density of 92mW/cm2 for 4 h.

Alumina supported Pt group metal monolithic catalysts were investigated for selective oxidation of CO in hydrogen-rich methanol reforming gas for proton exchange membrane fuel cell (PEMFC) applications. The results are described and discussed in the present paper and show that Pt/γAl2O3Pt/γAl2O3 was the most promising candidate to selectively oxidize CO from an amount of about 1 vol% to less than 100 ppm. We have investigated the effect of the O2 to CO feed ratio, the feed concentration of CO, the presence of H2O and/or CO2, and the space velocity on the activity, selectivity and stability of Pt/Al2O3 monolithic catalysts. Afterwards, the Pt/Al2O3 catalyst was scaled up and applied in 5 kW hydrogen producing systems based on methanol steam reforming and autothermal reforming. The hydrogen produced was then used as fuel for an integrated PEMFC.

An exergy analysis of methanol autothermal generating hydrogen system for PEMFC is presented. The process combines a catalytic combustion heat exchanger (CCHE), using partial off-gases containing hydrogen as feedstock, with an auto-thermal reformer (ATR), two water gas shift (WGS) reactors and four preferential oxidation (PROX) reactors. Energy and exergy of system were calculated and analyzed. The results demonstrated that inner exergy losses resulted from the irreversible heat transfer and reaction were the dominant factors. The most important destruction of exergy within the system was found to occur in the reformer and the catalytic combustion heat exchanger. Their ratios of exergy loss accounted for 25.03% and 24.95%, respectively, of the whole system. Based on results of thermodynamic and exergetic analysis, the reformer was optimized. The optimal W/MW/M (molar water to methanol) is around 1.5–2.0 and A/MA/M (molar air to methanol) is around 1.5. Certain recommendations were posed. The conclusions could help to optimize methanol autothermal generating hydrogen system for PEMFC.

A compact plate-fin reformer (PFR) consisting of closely spaced plate-fins, in which endothermic and exothermic reactions take place in alternate chambers, has been studied. In the PFR, which was based on a plate-fin heat exchanger, catalytic combustion of the reforming gas, as a simulation of the fuel cell anode off gas (AOG), supplied the necessary heat for the reforming reaction. One reforming chamber, which was for hydrogen production, was integrated with two vaporization chambers and two combustion chambers to constitute a single unit of PFR. The PFR is very compact, easy to be placed and scaled up. The effect of the ratio of H2O/CH3OHH2O/CH3OH on the performance of the PFR has been investigated, and temperature distributions in different chambers were studied. Besides, the stationary behavior of the PFR was also investigated. Heat transfer of the reformer was enhanced by internal plate-fins as well as by external catalytic combustion, which offer both high methanol conversion ratio and low CO concentration. In addition, the fully integrated reformer exhibited good test stability. Based on the PFR, a scale-up reformer was designed and operated continuously for 1000 h, with high methanol conversion ratio and low CO concentration.

CuO/ZnO/CeO2-ZrO2 catalysts for methanol steam reforming (MSR) were prepared by a co-precipitation procedure, and the effects of precipitation aging time on the catalytic performance were investigated. It was found that the prolonged precipitation aging time increased the surface Cu atoms and improved the reducibility of catalyst, but decreased the oxygen storage capacity. A nearly linear increase between the surface Cu atoms and H2 production rate was obtained in prepared CuO/ZnO/CeO2-ZrO2 catalysts with prolonged precipitation aging time. However, CO concentration increased with the decrease of the oxygen storage capacity. Considering the H2 production rate and CO level, the optimal precipitation aging time was 2 h. CuO/ZnO/CeO2-ZrO2 prepared using this aging time exhibited the best activity with suppressed CO formation.

A series of Ru/Ce0.8Zr0.2O2 catalysts were prepared by the impregnation method with Ce0.8Zr0.2O2 homoprecipitated and calcined at different temperatures as supports. The supports and the catalysts were characterized with TG-DSC, BET and H2-TPR techniques. It was shown that the Ce0.8Zr0.2O2 calcined at 500°C formed Ce-Zr solid solution and had a proper surface area and pore opening and a weak interaction with Ru species, leading to a significant increase in the catalytic activity. A suitable reduction methods promoted distribution of active species. The Ru/Ce0.8Zr0.2O2 prepared with the Ce0.8Zr0.2O2 calcined at 500°C showed high activity after calcination at 400°C and successive reduction with H2N·NH2·H2O and H2. It gave a H2 conversion of 93.57%, approaching to the equilibrium value under the conditions of 290°C, 0.1 MPa, 10000 h−1 and H2/CO2 molar ratio of 3.5.

The supported Rh/MgO/Ce0.5Zr0.5O2 catalysts were developed for autothermal reforming of methane. The effects of ceria–zirconia addition on the Rh catalyst were characterized with BET, XRD, SAED, HREM and TPR. The catalytic performance was evaluated on a flow through reactor. Results showed that the addition of ceria–zirconia enhanced the catalyst stability due to the interactions between ceria–zirconia, MgO promoter and the active component Rh. Meanwhile, the selectivity towards hydrogen in reformate was also boosted because of the increased water gas shift activity by the mixed oxides. The results also showed that the structural properties, the textural properties and the redox properties of ceria–zirconia had great influences on the catalyst performance, especially on the catalyst stability. Formations of single phase solid solution, larger pore size as well as Ce/Zr ratio at 1/1 were more desirable for ceria–zirconia dopant. As a result, one of the optimized honeycomb catalysts with the composition of 0.3% Rh/2.5% MgO/43.2% Ce0.5Zr0.5O2/54.0% cordierite (wt.%) has been continually operated at 800 °C up to 2000 h without deactivation.

This paper presents an experimental investigation on influence of liquid physical properties and channel diameter on gas–liquid flow patterns in horizontal circular microchannels with inner diameters of 302, 496 and 916 μm. Several liquids with different physical properties, i.e. water, ethanol, three sodium carboxymethyl cellulose (CMC) solutions (0.0464%, 0.1262%, 0.2446% CMC) and two sodium dodecyl sulfate (SDS) solutions (0.0608%, 0.2610% SDS) are chosen as working fluid and nitrogen as working gas. By using a high-speed photography system, flow patterns such as bubbly flow, slug and unstable slug flow, churn flow, slug-annular and annular flow are observed and identified on the flow regime maps. The results show that the liquid physical properties (viscosity and surface tension) and channel diameter affect the flow pattern transitions remarkably. Comparison with existing models in literature implies that these transitions cannot be well predicted. As a result, an effort is put into the proposition of a new empirical model taking the effects of channel size and liquid physical properties into account.Highlights► Gas–liquid two-phase horizontal flow in circular microchannel was investigated. ► Two-phase flow regime maps were developed. ► Influence of diameter and liquid physical properties on flow patterns were discussed. ► New empirical flow pattern transition model was proposed.

CO2 adsorption and methanation on a Ni/Ce0.5Zr0.5O2 catalyst has been investigated using in situ FTIR spectroscopy. CO2 adsorption and methanation experiments were conducted on both components of the support and the catalyst to identify the adsorption species and any intermediate species. It was proposed that CO2 prefers to adsorb on surface oxygen sites adjacent to Ce(III) compared with those adjacent to Ce(IV)/Zr or surface hydroxyl sites. Five adsorption species were revealed for CO2 adsorption on Ni/Ce0.5Zr0.5O2 and monodentate carbonates formed on Ce(III) are easier to be hydrogenated than those on Ce(IV). Formate species were found to be the main intermediate species during the reaction and Ce(III) sites were proposed to be active sites for their hydrogenation. The adsorption and hydrogenation of formic acid were also conducted to confirm the identification of the intermediate species during the reaction. –CH2OH species were detected for the first time and found to be the further intermediates in the reaction.

A WO3/CeO2-ZrO2 catalyst system was discovered for selective catalytic reduction of NOx with NH3; the catalyst (10 wt% WO3 loading) showed nearly 100% NOx conversion in a temperature range of 200–500 °C, at a space velocity of 90000 h−1 in a simulated diesel exhaust containing 550 ppm NOx (NO : NO2 feed ratio at 1.0), 10 vol% H2O and 10 vol% CO2; the catalyst also exhibited high temperature stability.

Metal–organic frameworks (MOFs), assembled by metal ions or their clusters and organic linkers, are one of the state-of-the-art crystalline materials. Their features such as ultra-high porosity, synthetic tailorability and relative ease of synthesis make them promising candidates for diversified applications. Controllable integration of MOFs and carbon-based materials not only leads to further enhancement of single-phase MOFs in terms of stability and electrical conductivity, but also surprisingly brings about a number of new functionalities like formation of new pores and template effects. These benefits allow the resultant MOF–carbon composites to be applied beyond the fields of single-phase MOFs. Increasing research interests have been aroused in this rapidly developing interdisciplinary area. This review aims to specifically group together the important reports focused on MOF–carbon composites till now. The methods used for composite synthesis and applications of the composites are investigated and categorized. The review also exclusively discusses the functionalities stemming from the synergistic effects of the two intriguing materials and pictures the future prospects at the end.