New hierarchical composites containing micropores and mesopores were synthesized by assembling HKUST-1 (Cu3(BTC)2) on siliceous mesocellular foams (MCFs). The structure, morphology, and textural properties of as-prepared composites were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and N2 sorption isotherms, respectively. The results suggest that the coexistence of mesoporous silicas promotes the formation of nanosized MOFs, and the mesostructures of silicas are not destroyed by MOFs. Moreover, the micropore/mesopore volume ratio can be controlled by varying the amounts of MOFs. The CO2 adsorption capacities were calculated by breakthrough curves, which were tested in a fixed bed. The CO2 adsorption capacity of the composites reaches 1.40 mmol/g, which is higher than that of bulk HKUST-1. The structure and CO2 adsorption capacity of the composites after the hydrothermal treatment also have been evaluated. The results show that composite-2 has a larger CO2 adsorption capacity of 1.68 mmol/g after steam conditioning and that the structure of HKUST-1 in the composites remain stable.

Two micromesoporous composites of MCM-41/13X are synthesized through a two-step crystallization process and a one-step crystallization process, respectively. The results of X-ray diffraction, nitrogen adsorption–desorption isotherms, Fourier transform infrared spectroscopy, and transmission electron microscopy results show that the as-prepared samples possessed both micropores and mesopores. The materials take advantage of not only the large adsorption capacity and thermal stability of the microporous material, but also the rapid diffusion and mass transfer of mesoporous materials, which lead to improve CO2 adsorption capacities compared to the pure microporous or mesoporous materials.

•Fe–Zr mixed oxides with different Fe content are prepared by sol-gel method.•The introduction of iron favors the formation of moderately acidic and basic sites.•The moderately acidic and basic sites could effectively activate CO2 and methanol.•The amount of moderately acidic and basic sites linearly relate to the DMC yield.A series of Fe–Zr mixed oxides with different Fe content were prepared and used for direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol. The best catalytic performance was achieved over the Fe0.7Zr0.3Oy catalyst, with DMC yield of 0.44 mmol·gcat−1 and DMC selectivity of 100% under the reaction conditions of 110 °C and 12 MPa. Characterization results of N2 physisorption, XRD, XPS, TPR and NH3/CO2-TPD indicated that the Fe–Zr mixed oxides with coexistence structure of hexagonal Fe2O3 and cubic Fe2O3 favored the formation of moderately acidic and basic sites, which then improved the activation of CO2 and methanol. The DMC yield was shown to be linearly related to the amount of moderately acidic and basic sites.The introduction of Fe to ZrO2 increases the amount of moderately acidic and basic sites, which then favors the activation of methanol and CO2 and improves the catalytic activity of dimethyl carbonate (DMC) synthesis.Download high-res image (140KB)Download full-size image

A series of mesoporous NiO–Y2O3–Al2O3 composite oxides with different yttrium contents were synthesized by either a one-pot evaporation-induced self-assembly (EISA) method or impregnation for carbon dioxide reforming of methane (CRM). Their catalytic performance was evaluated and all the samples were characterized by means of N2 physisorption, XRD, XPS, H2-TPR and TEM. It was found that addition of appropriate amounts of Y2O3 (sample NYA2) has little influence on the EISA process, and thus, an ordered mesoporous structure with enhanced textural and Ni dispersive properties can be obtained. The NYA2 catalyst showed excellent performance in CRM, and no deactivation was observed for 100 h. Based on the comparative characterization of the reduced and exhausted catalysts, the good performance of NYA2 was related to its low carbon formation rate thanks to the very small and thermally stable metallic Ni particles (ca. 6.0 nm) which were well embedded in the catalyst framework and the redox properties of the Y2O3 promoter.

In this work, the equilibrium adsorption and the kinetic adsorptive breakthrough curve model have been established for CO2 adsorption on K-based sorbent. The equilibrium adsorption of CO2 on the studied K-based sorbent has been developed by several adsorptive equilibrium models to meet the perfect description of the adsorption performance of the K-based sorbent. Then, the kinetic breakthrough curve model is established on the basis of the equilibrium adsorptive model over a fixed bed, whereas the mass balance, the adsorptive equilibrium, and the kinetics of mass transfer with linear driving force (LDF) model have been taken into account to derive the partial differential equations of CO2 adsorption on the K-based sorbent. Moreover, the factors of both molecular diffusion (DA) and Knudsen diffusion (DK) have been considered with the internal mass transfer coefficient to describe the internal structure of K-based sorbent. The model results reveal that the kinetic model developed in this work strongly agrees with the experimental results. Consequently, the adsorption equilibrium of the Freundlich isotherm model has been selected, and the parameters of the model have been determined with values of 1.8221/1.6118 and 0.0874/0.1095 for KL and n, respectively. Furthermore, the analysis for the influence of mass transfer coefficients on the predicted breakthrough curve reveals that the internal mass transfer coefficient is more sensitive than the external mass transfer coefficient.

Zn/Al/La and Zn/Al/La/M (M = Li, Mg, Zr) mixed oxides were obtained by calcination of hydrotalcite precursors and tested for glycerol carbonate (GC) synthesis from CO2 carbonylation. The results indicated the catalytic activity may be associated with the large specific surface area, the high surface content of Zn and the high binding energy of Zn atoms as well as the high density of moderately basic sites. The good result was obtained on the catalyst with a molar ratio of Zn:La:Al = 4:1:1 and, within a certain range, glycerol conversion and GC yield increase linearly upon the increase of the density of moderately basic sites. In addition, the catalytic activity was obviously improved upon introduction of Li, Mg and Zr. The effect of reaction parameters on the carbonylation of glycerol was also studied. The DRIFTS results suggest that the activated CO2 may be in the form of a bridged bidentate carbonate that inserts into zinc glycerolate to form an intermediate species of a seven-membered ring ester followed by intramolecular rearrangement to produce GC. Theoretical calculation results indicated that the seven-membered ring ester has good stability and the formation process happens spontaneously.

A series of La–Mn–Zn–Cu–O based perovskite ceramic precursors were prepared and characterized by XRD, N2-adsorption, SEM, H2-TPR, N2O-adsorption, XPS and TPD techniques. Both La2CuO4 and LaMnO3 perovskite structures were observed for the materials and more defects and the “metal-on oxide” can be realized via reduction. It was found that the samples with both La2CuO4 and LaMnO3 structures showed better catalytic performance for methanol synthesis from CO2/H2. Higher methanol selectivity might due to the appearance of Cuα+ that derived from the abundant defects of perovskite structure. The ratio of both Cuα+ and Cu0 species to the total copper species was the significant factor for the CO2 conversion.

•La2CuO4 perovskite catalysts are prepared and tested.•The promoter Y, Ce, Mg, Zr can improve the performance of perovskite catalysts.•The perovskite catalysts show high selectivity for methanol.•The conversion of CO2 depends on the surface area of metallic Cu.A series of La–M–Cu–Zn–O (M = Y, Ce, Mg, Zr) based perovskite-type catalysts are prepared by sol–gel method and characterized by XRD, BET, TPR, N2O-adsorption, XPS and TPD techniques. The results indicate that all the catalysts exhibit La2CuO4 perovskite structure. The addition of Ce, Mg and Zr lead to smaller particles, lower reduction temperature, higher Cu dispersion, larger amount of hydrogen desorption at low temperature and more amount of basic sites. However, Y has less affects on the physicochemical properties. The catalysts derived from perovskite-type precursors show high selectivity for methanol, which is correlated with the Cuα+ species that exists in the reduced catalysts. More exposed Cu surface area is favorable for high CO2 conversion.

•Various silicas are obtained in the TMB–P123–H2O–TEOS quadru-component system.•MLVs are developed from HEX structure and eventually evolve into MCF structure.•The phase transition process of various silicas is explained by packing parameter.Various siliceous structures were obtained using a nonionic block copolymer (Pluronic P123) surfactant and trimethylbenzene (TMB) as a hydrophobic additive by hydrolysis and condensation of tetraethoxysilane (TEOS) in a sol–gel process. The resultant materials were characterized by small-angle X-ray diffraction (SAXRD), nitrogen adsorption analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed the structure transformation from hexagonal structure (HEX) to multilamellar vesicles (MLVs) and then to mesocellular foams (MCFs) in the TMB–P123–H2O–TEOS quadru-component system. The morphology of the mesoporous silica was mainly controlled by the mass ratio of TMB/P123 resulted from the increasing volume of the hydrophobic chain of micelle of P123 that caused by more amount of TMB dissolved in the PPO segment of polymer. The fact that the occurrence of rod-like particles with curved ends and the coexistence of the MLVs and the HEX structure indicates that the MLVs are developed from the ends of HEX structures, rather than formed by a direct cooperative self-assembly mechanism. Further increasing of packing parameter of surfactant resulted from TMB addition transforms lamellar micelles to reversed micelles, leading to the formation of MCFs.

Thermochemical CO2 splitting was carried out over ceria/zirconia solid solutions prepared via a P123-added hydrothermal method in the temperature range of 1100–1400 °C. XRD, Raman and TPR characterization indicated that the introduction of Mg and Ca into ceria/zirconia could produce lattice defects in the fluorite lattice, and then strongly modify the mobility of oxygen as well as the thermal stability of the samples. As compared to Mg-doped samples, faster reaction rates and higher CO2 splitting reactivity were obtained over Ca-doped samples, because of the faster oxygen mobility in Ca–Ce–Zr–O ternary solid solutions. Moreover, the porous structure with small particle size favoured the thermal reduction and the mass diffusion. As a result, fast reaction rates and relatively high fuel productivity were obtained at the moderate thermal reduction temperature (1200 °C).

Mesoporous MgAl(O) sorbents with different Mg/Al molar ratios (0, 0.5, 1.0, 1.5) were synthesized via a one-step surfactant assisted precipitation method. The structural properties of these sorbents were systematically characterized by XRD, SEM, FT-IR, N2 adsorption–desorption and CO2-TPD. The CO2 adsorption–desorption performance of the sample was studied in a fixed-bed reactor. The results showed that the xMgAl(O) sorbents possessed a mesoporous structure, high specific surface areas and abundant basic sites. In the synthesis process, Mg and Al species interacted with P123 to form PEO-Mn+-anions that promoted the dispersion of MgO on the Al2O3. The XRD, FT-IR and CO2-TPD results showed that the MgO was not only dispersed on Al2O3, but enters the Al2O3 framework, resulting in more exposed basic sites for CO2 adsorption. In the CO2 adsorption process, the CO2 adsorption capacity of the sorbent was related to the amount of basic sites and the specific surface area. The CO2 uptake of the sorbent significantly improved in the presence of water vapor. Results of a cycling test suggested that the sorbent was stable in multiple adsorption–desorption cycles.

Doped La–M–Mn–Cu–O based (M = Ce, Mg, Y, Zn) perovskite materials were prepared by the sol–gel method and characterized by XRD, N2-adsorption, ICP-OES, SEM, TPR, N2O-adsorption, XPS and TPD techniques. Upon the introduction of the fourth elements, all the samples keep the stable LaMnO3 perovskite structure, and part of the copper species is separated from the perovskite lattice. More structure defects, lower reduction temperature and better low-temperature H2 adsorption on the unit surface area are observed. In the application for methanol synthesis from CO2/H2, the Zn doped catalyst showed better performance which may because the strength of the weak basic sites play a significant role on methanol selectivity and the amount of H2 adsorbed on the unit surface area is the key for CO2 conversion.

The transformation of CO2 and glycerol into glycerol carbonate was carried out by using acetonitrile as coupling agent over La2O2CO3–ZnO in the present work. A series of La–Zn mixed oxide catalysts with different molar ratios were prepared and calcined at different temperatures. The catalysts were characterized by N2 physisorption, XRD, XPS, FT-infrared spectroscopy and temperature-programmed desorption of CO2. The results revealed that the formation of La2O2CO3 improved the surface basicity which then favors the CO2 activation and the carbonate yield was shown to be correlated with the amount of moderately basic sites. The XPS measurement demonstrated that La2O2CO3 favored the electron transfer from zinc atoms to lanthanum atoms or oxygen atoms which then favors the activation of glycerol. The synergism between ZnO and La2O2CO3 is responsible for the high catalytic activities of the La–Zn catalysts. The best result was obtained on the catalyst with molar ratio of La:Zn = 1:4 and calcination at 500 °C.

Separation of dimethyl carbonate/methanol azeotropic mixture by using distillation process has been a hot-point in the study of the synthesis process of dimethyl carbonate by urea methanolysis method. Most studies focus on the steady-state design, and only few papers have dealt with the dynamic performance and control of this binary azeotropic system. This paper explores the design and control of pressure-swing distillation systems for separation of dimethyl carbonate/methanol. The steady-state and dynamic simulations are carried out with Aspen Plus and Aspen Dynamics. Then, on the basis of the global economical analysis, an optimized separation configuration is proposed. The vital operating parameters and geometric parameters are determined according to the simulation and optimization results. Furthermore, two control strategies, CS1 and CS2, are proposed. With disturbance, the proposed basic control structure (CS1) can only maintains the quality specification of products from the bottom of the first column. However, the second control structure (CS2) succeeds in holding the bottom product purity for two distillation columns, even for large feed flow rate and large composition disturbances. Detailed analysis for CS1 and CS2 is made based on dynamic simulation which illustrates that the control structure CS2 outperforms CS1 to handle the disturbances.

Mesoporous Mg–Zr solid solutions with different nominal Mg/Zr atomic ratios (0, 0.25, 0.5, 0.75, 1) were synthesized by a coprecipitation method, and the performance of CO2 adsorption/desorption was studied in a fixed-bed reactor under different conditions. In the synthesis process, Mg2+ was introduced successfully into the ZrO2 lattice and formed a maximum number of new Mg–O–Zr basic sites at Mg/Zr = 0.5. The CO2-temperature-programmed desorption (TPD) results showed the basic strength of the basic sites was Zr–O–Zr < Mg–O–Zr < Mg–O–Mg and the relatively weak basic strength of Mg–O–Zr was a benefit for regeneration of the sorbent. In the process of adsorption, high surface area (269 m2/g) and pore volume (0.63 m3/g) as well as appropriate basic sites of Mg–O–Zr made the Mg–Zr solid sorbent increase CO2 adsorption capacity by more than 5 times compared to pure MgO. The CO2 adsorption capacity of the sorbent increased in the presence of water vapor. Typically, the CO2 capacity of Mg–Zr solid sorbent had a maximum CO2 capture of 1.28 mmol/g at 30 °C without water vapor and 1.56 mmol/g sorbent under 10 vol % moist conditions at 60 °C, respectively. Results of a reutilization test suggested that the sorbent was stable for cyclic adsorption.

A novel sorbent, MgO/Al2O3-supported K2CO3, for CO2 sorption was prepared. It was found that the sorbent prepared by the multi-impregnation method showed a large CO2 capture capacity at low temperature under simulated flue gases with MgO loading of 10 and 20 wt % (KMgAlI3010 and KMgAlI3020). The presence of water vapor pretreatment and MgO loadings had different effects on the CO2 adsorption mechanisms. For the KMgAlI3010 sorbent, the main phase was KHCO3 after CO2 adsorption. While for the KMgAlI3020 sorbent, when pretreated with less steam, the main phase was Mg2Al2(CO3)4(OH)2·15H2O after CO2 adsorption. When pretreated with excess steam, however, the CO2 adsorption mechanism was similar to the KMgAlI3010 sorbent. Furthermore, the as-prepared KMgAl sorbents were stable even after 30 adsorption/desorption cycles.

This article reviews the progress made in CO2 capture, storage, and utilization in Chinese Academy of Sciences (CAS). New concepts such as adsorption using dry regenerable solid sorbents as well as functional ionic liquids (ILs) for CO2 capture are thoroughly discussed. Carbon sequestration, such as geological sequestration, mineral carbonation and ocean storage are also covered. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers which offers a way to mitigate the increasing CO2 buildup is introduced.Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Progress on CO2 capture, storage, and utilization (CCSU) in Chinese Academy of Sciences (CAS) were reviewed. ► The main advantages and disadvantages of the CCSU process were discussed. ► The further research directions of CCSU were proposed.

•Detailed investigation on the mechanism for the formation of the Zn(NCO)2(NH3)2 in urea methanolysis.•Direct pathway in which urea is activated by ZnO is more favorable.•The dissolution of ZnO in urea methanolysis my due to the formation of the catalytic active species Zn(NCO)2(NH3)2.The mechanism for the formation of Zn(NCO)2(NH3)2 in the process of urea methanolysis is investigated by using density functional theory(DFT). Two paths have been proposed and simulated to investigate the formation process. For path 1, two urea molecules are adsorbed on the ZnO surface. Then, two surface-adsorbed urea molecules dissociate from the surface accompanied by the breakage of ZnO bonds, followed by the Zn(NCO)2(NH3)2 formation after NH3 combination to the Zn(NCO)2 complex. For path 2, two molecules of HNCO and NH3 are formed after a urea self-dissociation process. Then, the four molecules are adsorbed on the ZnO surface and form the product Zn(NCO)2(NH3)2 and H2O. Comparing the exothermic data and the highest energy barrier of the two paths, path 1 release more energy and its highest energy barrier is 3.7 kcal/mol lower than that in path 2. In conclusion, path 1 is a more favorable way for the formation of Zn(NCO)2(NH3)2 complex.Download high-res image (107KB)Download full-size image

A series of sulfonato-salen metal complexes were intercalated into Mg-Al layer double hydroxide (LDH) and used for selective oxidation of glycerol to dihydroxyacetone (DHA). The X-ray diffraction, Fourier transform infrared spectroscopy and elemental analysis results of the as-prepared catalysts demonstrated that the metal ions were combined with sulfonato-salen ligands to form metal complexes that intercalated in the LDH. The Cr(III) and Cu(II) sulfonato-salen complex-intercalated LDH catalysts were favorable for activation of H2O2, promoting the oxidation of glycerol to DHA. It was found that the Cu(II) sulfonato-salen-intercalated LDH catalyst was also beneficial for the dehydrogenation of glycerol, resulting in a high selectivity to DHA. The glycerol conversion and DHA selectivity obtained over the Cu(II) sulfonato-salen-intercalated LDH catalyst reached 40.3% and 52.9% respectively under the optimum reaction conditions of 60°C, 4 h and pH value 7.

The thermochemical CO2 splitting activity of NiFe2O4 and NiFe2O4/ZrO2 prepared by the conventional co-precipitation method was investigated with thermogravimetric analysis (TGA) technique. Significant sintering was observed over the two samples during cyclic reactions because of the high reaction temperature. This would lead to an incomplete re-oxidation of the reduced sample in the CO2 splitting reaction. Introduction of ZrO2 could greatly enhance the thermal stability of NiFe2O4, and hence, the cycling behavior in repeated cycles. The catalytic results of NiFe2O4/ZrO2 for cyclic splitting of CO2 in a high-temperature furnace indicate that CO productivity increased with the thermal reduction temperature, while the cycling stability severely decreased with the cyclic number.

A series of Cu/Zn/Al/Zr hydrotalcite-like precursors with Zr4+:(Al3++Zr4+) from 0 to 0.7 were synthesized by a co-precipitation method. X-ray diffraction and thermogravimetric measurements demonstrated that the yield of the hydrotalcite-like phase decreases with increased Zr content. The Cu/Zn/Al/Zr mixed oxides were then obtained by calcination of the hydrotalcite-like precursors and tested for methanol synthesis from CO2 hydrogenation. With increased Zr4+:(Al3++Zr4+) atomic ratio, the exposed Cu surface area and dispersion of Cu first increase until Zr4+:(Al3++Zr4+) = 0.3 and then decrease. However, the total number of basic sites on catalysts increases continuously. It is also found that the CO2 conversion is related to the exposed Cu surface area and the dispersion of Cu, while the CH3OH selectivity is related to the distribution of basic sites on the catalyst surface. The incorporation of a suitable amount of Zr is beneficial for the production of methanol, and the best catalytic performance is obtained when the Zr4+:(Al3++Zr4+) atomic ratio is 0.3.Graphical abstractWith increasing Zr content, the exposed Cu surface area first increases until Zr4+:(Al3++Zr4+) = 0.3 and then decreases, and the proportion of strongly basic sites shows a similar trend, except for Zr4+:(Al3++Zr4+) = 0.7. Both the CO2 conversion and the CH3OH selectivity exhibit a volcano trend with increasing Zr content.Download high-res image (72KB)Download full-size imageHighlights► The introduction of Zr affects the Cu surface area and Cu dispersion of catalyst. ► The introduction of Zr affects the surface basicity of the reduced catalyst. ► The CO2 conversion is related to the Cu surface area and Cu dispersion of catalyst. ► The methanol selectivity is related to the distribution of basic sites of catalyst. ► The incorporation of suitable amount of Zr is favor for the catalytic performance.

•Zn–Mg mixed oxide catalysts were prepared via urea–precipitation.•ZM0.25 exhibited high catalytic activity within 30 min (PC yield 94.8%).•PC yield was strongly related to alkaline of unit specific surface area.•ZM0.25 catalyst can be reused for up to 5 times (PC yield > 97%).Zn/Mg catalysts with different atomic ratios of zinc to magnesium were prepared via urea–precipitation. The products were characterized by XRD, BET, SEM, CO2-TPD, and ICP. Compared with pure ZnO, the mixed oxide possessed appropriate alkaline density and high specific surface area. The catalyst with Zn/Mg of 1:4 exhibited high catalytic activity within 30 min and reliable production for propylene carbonate (PC) (94.8%). It was found that the PC yield was strongly related to the amount of alkali of unit specific surface area. Furthermore, the regeneration of ZnO–MgO catalyst was investigated and the ZM0.25 catalyst can be reused for up to 5 times with less changed PC yield.Download full-size image

A series of mesoporous NiO–Y2O3–Al2O3 composite oxides with different yttrium contents were synthesized by either a one-pot evaporation-induced self-assembly (EISA) method or impregnation for carbon dioxide reforming of methane (CRM). Their catalytic performance was evaluated and all the samples were characterized by means of N2 physisorption, XRD, XPS, H2-TPR and TEM. It was found that addition of appropriate amounts of Y2O3 (sample NYA2) has little influence on the EISA process, and thus, an ordered mesoporous structure with enhanced textural and Ni dispersive properties can be obtained. The NYA2 catalyst showed excellent performance in CRM, and no deactivation was observed for 100 h. Based on the comparative characterization of the reduced and exhausted catalysts, the good performance of NYA2 was related to its low carbon formation rate thanks to the very small and thermally stable metallic Ni particles (ca. 6.0 nm) which were well embedded in the catalyst framework and the redox properties of the Y2O3 promoter.

The transformation of CO2 and glycerol into glycerol carbonate was carried out by using acetonitrile as coupling agent over La2O2CO3–ZnO in the present work. A series of La–Zn mixed oxide catalysts with different molar ratios were prepared and calcined at different temperatures. The catalysts were characterized by N2 physisorption, XRD, XPS, FT-infrared spectroscopy and temperature-programmed desorption of CO2. The results revealed that the formation of La2O2CO3 improved the surface basicity which then favors the CO2 activation and the carbonate yield was shown to be correlated with the amount of moderately basic sites. The XPS measurement demonstrated that La2O2CO3 favored the electron transfer from zinc atoms to lanthanum atoms or oxygen atoms which then favors the activation of glycerol. The synergism between ZnO and La2O2CO3 is responsible for the high catalytic activities of the La–Zn catalysts. The best result was obtained on the catalyst with molar ratio of La:Zn = 1:4 and calcination at 500 °C.

Zn/Al/La and Zn/Al/La/M (M = Li, Mg, Zr) mixed oxides were obtained by calcination of hydrotalcite precursors and tested for glycerol carbonate (GC) synthesis from CO2 carbonylation. The results indicated the catalytic activity may be associated with the large specific surface area, the high surface content of Zn and the high binding energy of Zn atoms as well as the high density of moderately basic sites. The good result was obtained on the catalyst with a molar ratio of Zn:La:Al = 4:1:1 and, within a certain range, glycerol conversion and GC yield increase linearly upon the increase of the density of moderately basic sites. In addition, the catalytic activity was obviously improved upon introduction of Li, Mg and Zr. The effect of reaction parameters on the carbonylation of glycerol was also studied. The DRIFTS results suggest that the activated CO2 may be in the form of a bridged bidentate carbonate that inserts into zinc glycerolate to form an intermediate species of a seven-membered ring ester followed by intramolecular rearrangement to produce GC. Theoretical calculation results indicated that the seven-membered ring ester has good stability and the formation process happens spontaneously.