This work examines CO2 adsorption over various N-substituted/grafted graphanes to identify the promotional effects of various N-functionalities have on the adsorption characteristics using DFT. CO2 adsorbs weakly on a graphane surface functionalized with a single, isolated substituted N- or grafted NH2-sites. The presence of coadsorbed H2O on the surface promotes CO2 adsorption on both N- and NH2-sites, with highly exothermic adsorption energies (∼−50 kJ mol–1). Directly grafted −NH2 or −OH functional groups on C atoms adjacent to C atoms which have a −NH2 group grafted suffer from geometrical restrictions preventing dual stabilization of formed carbamate upon adsorption of CO2. CO2 adsorption can be greatly enhanced with the presence of a −OH group or second −NH2 group in the proximity of a −NH2 site on graphane, and only if a n(−CH2−) (n ≥ 1) linker is introduced between the −NH2 or −OH and graphane surface (adsorption energies of −58.8 or −43.1 kJ mol–1 at n = 2). The adsorption mechanistics provided by DFT can be used to guide the atomic-level rational design of N-based graphane and carbon adsorbents for CO2 capture.

Efficient separation and transfer of photogenerated electron/hole as well as enhanced visible light absorption play essential roles in photocatalytic reactions. To promote the photocatalytic reduction of Cr(VI), a toxic heavy metal ion, multiwalled carbon nanotube (MWCNT) was introduced as an electron acceptor into NH2-MIL-68(In). This led to the growth of a willow leaf-like metal-organic framework (MOF) on an MWCNT backbone forming MWCNT/NH2-MIL-68(In) (PL-1), which showed a highly efficient transfer of photogenerated carriers. Moreover, MWCNT incorporation introduced more mesopores for Cr(VI) diffusion and enhanced the visible light adsorption without lowering the conduction band position. As a result, the photocatalytic kinetic constant of PL-1 was found to be almost three times higher than that of the parent NH2-MIL-68(In). Thus, growing MOFs on MWCNTs provides a facile and promising solution for effective remediation of environmental pollution by utilizing solar energy. This work provides the first example of using MWCNT/MOF composites for photocatalytic reactions.

•A novel [O]-induced reactive adsorptive desulfurization approach was proposed.•Over 90% of thiophenic compounds can be removed within 10 min (6 h−1) by RADS.•Desulfurization capacity by RADS reached 4.4 times of that by conventional ADS.•Desulfurization selectivity enhanced 2.4 orders of magnitude.•RADS mechanism and preferential catalytic/adsorption sites were clarified.The development of processes for clean energy production with low energy consumption is a central strategy for a sustainable and environmentally friendly planet. Here we report a novel [O]-induced reactive adsorptive desulfurization (RADS) approach for ultra-clean fuel production using multifunctional AgXO@SBA-15 adsorbent with and without the addition of air under ambient conditions. The adsorption capacity of AgXO@SBA-15 by RADS reached 4.4 times of that by conventional ADS from low-sulfur fuel (10 ppm-S), and its adsorption selectivity was enhanced 2.4 orders of magnitude. Over 90% of sulfur was removed within 10 min (corresponds to the space velocity of 6 h−1). The RADS mechanism was illustrated as a simultaneous oxidation of thiophenic compounds (to sulfones) and the selective adsorption of sulfones, where the nano-sized silver species detected at different valence states (AgO, Ag2O and Ag) and the fed air played the versatile enabling roles as the oxidation catalyst and the oxidant, respectively, and the surface silanol groups were suggested as the preferential adsorption sites for the sulfones yielded. The work may open up new avenues for developing supported metal oxides for ultra-clean fuel production under ambient conditions, taking advantage of self-retained [O] and/or introduced earth-abundant air.Download high-res image (70KB)Download full-size image

A composite of Cu-BTC and graphite oxide (GO) was prepared by rapid room-temperature synthesis method for thermally driven adsorption chillers (TDCs). A series of composites Cu-BTC@GO with varied GO loading were synthesized at room temperature within 1 min, and characterized by N2 adsorption test, scanning electron microscopy, powder X-ray diffraction, and Fourier transform infrared analysis. The adsorption isotherms of ethanol on the composites were measured at different temperatures, and then, the isosteric heats of ethanol adsorption were estimated. The composite working capacities and coefficient of performance (COP) of the composite–ethanol working pair were calculated for the application of refrigeration. Results showed that Cu-BTC@GO possessed a superhigh adsorption capacity for ethanol up to 13.60 mmol/g at 303 K, which was attributed to introduction of GO leading to increases in the surface dispersive forces and the mesoporous volume of Cu-BTC@GO. The isosteric heat of ethanol adsorption on Cu-BTC@GO was slightly higher than that of Cu-BTC. The adsorption capacity of Cu-BTC@GO was higher than many other metal–organic frameworks (MOFs) under the application conditions of TDCs. The composites exhibited 5.8–17.4% higher working capacity and energy efficiency than parent Cu-BTC for the application of refrigeration. The rapid room-temperature synthesis approach has potential for the preparation of new MOF-based composites.

•Proposed a new CADS–TiO2/SBA-15 system for ultra-deep desulfurization of fuel.•High CADS capacity of 12.7 mg/g at low S-conc. of 15 ppm-S was achieved.•Fast CADS kinetic equilibrium was achieved in 0.5 h.•Excellent regenerability of TiO2/SBA-15 by oxidative air treatment was reported.This study investigates catalytic adsorptive desulfurization (CADS) of model diesel fuel using TiO2/SBA-15 under mild conditions. The TiO2/SBA-15 was prepared by a facile incipient wetness impregnation method and characterized by N2 adsorption and X-ray diffraction. The CADS referred to ADS performance were evaluated in a batch reactor. High desulfurization uptake of 12.7 mg/g was achieved at low sulfur concentration of 15 ppmw-S by TiO2/SBA-15 under CADS, which was two-magnitude higher than that under ADS without the in-situ catalytic oxidation of dibenzothiophene. Kinetic results suggested that the CADS equilibrium over TiO2/SBA-15 was reached fast in 0.5 h. In the CADS–TiO2/SBA-15 system, the TiO2 loading, cumene hydroperoxide/dibenzothiophene ratio and CADS temperature were optimized to be 10 wt%, 2, and 35 °C, respectively. Furthermore, desulfurization tests in 5 consecutive CADS-regeneration cycles suggested that the bi-functional TiO2/SBA-15 can be regenerated by acetonitrile washing followed with oxidative air treatment. The CADS–TiO2/SBA-15 mechanism went through the oxidation of DBT to oxidized DBTO2 over TiO2/SBA-15 by cumene hydroperoxide, which was followed by the adsorption of the oxidized DBTO2 over TiO2/SBA-15. The superior desulfurization uptake at low sulfur concentration range, fast adsorption kinetics, excellent regenerability, operation at mild conditions, and facile and low-cost adsorbent synthesis make the CADS–TiO2/SBA-15 system an effective and economic desulfurization approach for ultra-clean fuel production.

Novel PEI-impregnated UiO-66 (PEI@UiO-66) composites with enhanced CO2 adsorption capacity and CO2/CH4 selectivity were synthesized and characterized. The dynamic CO2/CH4 separation performances were evaluated in the fixed bed. CO2 working capacity and CO2/CH4 selectivity of PEI@UiO-66 at 338 K were up to 1.65 mmol/g and 111, respectively, being 12.7 and 58 times greater than those of the parent UiO-66, respectively. In the presence of water vapor in feed stream, the CO2 capacity and CO2/CH4 selectivity of PEI@UiO-66 separately reached values of 2.41 mmol/g and 251, respectively, at a relative humidity (RH) of 55% and 338 K, having increases of 48.8% and 126%, respectively, in comparison with those under dry conditions, which were higher than many MOF-based adsorbents. Density functional theory (DFT) calculations suggested that the presence of water vapor promoted CO2 adsorption, likely because of the formation of bicarbonate with a lower amine/CO2 ratio than that required under dry conditions. The multiple adsorption-regeneration tests suggested that CO2 adsorption capacity of PEI@UiO-66 can be fully recovered after regeneration.

The objective of this work is to develop CuCl@AC adsorbent with high CO capacity and selectivity from CO/N2 binary gas mixture. A series of CuCl@AC adsorbents were prepared by a solid-state auto dispersion method, and then characterized by N2 adsorption test, XRD and XPS. CO and N2 adsorption isotherms on the adsorbents were measured by a volumetric method. The adsorption isotherms and selectivities of CuCl@AC adsorbents for CO/N2 binary mixture were estimated on the basis of ideal adsorbed solution theory (IAST). Results showed that (a) CO uptakes of CuCl@AC increased with CuCl loading in the loading range of 0–1.2 g/g. The maximal CO adsorption capacity of the CuCl@AC with CuCl loading of 1.2 g/g reached 38 cc/g at the P/P0 of 0.40, around 8 times of that over the original AC; (b) calcination time for the preparation of Cu(I)@AC had significantly impact on CO adsorption of the adsorbents due to valence change of Cu species on carbon surfaces. XPS analysis indicated that when the calcination time was optimized to be 1 h at 350 °C under argon, the prepared Cu(I)@AC had the highest percentage of Cu+ species on its surfaces, and consequently it had the highest CO capacity among the adsorbents since adsorptive species responsible for CO adsorption is Cu+; (c) The IAST-predicted CO/N2 adsorption selectivities of 1.2CuCl/AC decreased with pressure. Its CO/N2 selectivity was up to 100–450 at low pressure range of 0–10 kPa, and it remained in the range of 50–100 at higher pressure range of 20–100 kPa. The high adsorption capacity and selectivity of Cu(I)@AC adsorbents made it a promising adsorbent for CO/N2 mixture separation.

In this work, we explored a two-step oxidative desulfurization (ODS) approach using in-situ-generated peroxides in diesel by light irradiation. The supported catalysts were prepared by incipient wetness impregnation and characterized by N2 adsorption test, X-ray diffraction, and X-ray photoelectron spectroscopy. Kinetic curves for peroxide generation by light irradiation and self-decomposition over a MoO3/SiO2 catalyst were measured. Catalytic activities of the catalysts for ODS were tested. Results showed that (a) the efficiency of peroxide generation in diesel under a mercury lamp was much higher than that under a xenon lamp at the same light intensity and can be enhanced at a higher temperature, (b) with in-situ-generated peroxides in diesel by light irradiation, the ODS conversion of catalysts followed the order of MoO3/SiO2 > V2O5/SiO2 > WO3/SiO2 and the conversion reached 75.6% using the MoO3/SiO2 catalyst at the reaction temperature of 45 °C at the O/S ratio of 8, and (c) accompanying the main ODS reaction with hydroperoxides over the MoO3/SiO2 catalyst in diesel, the competing side reaction of peroxide self-decomposition occurred and its kinetics increased dramatically with the reaction temperature. The overall ODS conversion may be affected by the diffusion of bulky refractory sulfur compounds in diesel on the catalyst, which can be enhanced by increasing the pore size of the MoO3/SiO2 catalyst. The two-step oxidative desulfurization approach provides a viable path to achieve clean diesel effectively under mild conditions without using costly hydrogen.

This work examines CO2 adsorption over various N-substituted/grafted graphanes to identify the promotional effects of various N-functionalities have on the adsorption characteristics using DFT. CO2 adsorbs weakly on a graphane surface functionalized with a single, isolated substituted N- or grafted NH2-sites. The presence of coadsorbed H2O on the surface promotes CO2 adsorption on both N- and NH2-sites, with highly exothermic adsorption energies (∼−50 kJ mol–1). Directly grafted −NH2 or −OH functional groups on C atoms adjacent to C atoms which have a −NH2 group grafted suffer from geometrical restrictions preventing dual stabilization of formed carbamate upon adsorption of CO2. CO2 adsorption can be greatly enhanced with the presence of a −OH group or second −NH2 group in the proximity of a −NH2 site on graphane, and only if a n(−CH2−) (n ≥ 1) linker is introduced between the −NH2 or −OH and graphane surface (adsorption energies of −58.8 or −43.1 kJ mol–1 at n = 2). The adsorption mechanistics provided by DFT can be used to guide the atomic-level rational design of N-based graphane and carbon adsorbents for CO2 capture.

This work investigates adsorptive denitrogenation (ADN) of fuels over metal organic frameworks using a combined experimental/computational approach. MIL-101(Cr) shows high ADN capacities at low concentrations, ascribing to the sites on MIL-101(Cr) offering the strongest adsorption. Adsorption capacity of MIL-101(Cr) is higher for basic quinoline than that for nonbasic indole due to a greater adsorption strength of quinoline (−61.31 kJ/mol) than indole (−38.33 kJ/mol). Adsorption selectivity of various types of compounds in fuels follows the order of organonitrogen ≫ organosulfur > naphthalene, in good agreement with the order of adsorption strength as BEN (−62 ∼ −34 kJ/mol) < BES (−32 ∼ −24 kJ/mol) < BENap (−21.65 kJ/mol), suggesting MIL-101(Cr) is a highly selective adsorbent for ADN. ADN is negligibly affected by polyaromatic hydrocarbons, but suppressed by oxygenate cosolvent, that is, tetrahydrofuran to varied extents, depending on the varied adsorption mechanisms affected by N-types, including N-basicity, positive charge on H bound to N, and H-substitution.

This work investigates the adsorption of organosulfur compounds in model fuels over metal–organic frameworks (MOFs) using a combined experimental/computational approach. Adsorption isotherms of three MOFs, MIL-101(Cr), MIL-100(Fe), and Cu-BTC, follow the Langmuir isotherm models, and Cu-BTC shows the highest adsorption capacity for both dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), ascribing to the highest density of adsorption sites and fairly strong adsorption sites on Cu-BTC. Experimental results show adsorption selectivity of various compounds in model fuels follows the order of quinoline (Qu) > indole (In) > DBT > 4,6-DMDBT > naphthalene (Nap), which is consistent with the order of calculated binding energies. Adsorption capacities of thiophenic compounds decrease significantly with the introduction of Qu, In, or water due to their strong competitive adsorptions over the coordinatively unsaturated Cu sites on Cu-BTC. The binding energies of Qu, In, H2O, and DBT are calculated as −56.04, −41.01, −50.27, and −27.52 kJ/mol, respectively. The experimental and computational results together suggest that the adsorption strength of thiophenic compounds over Cu-BTC is dominated by the interaction of both the conjugated π system (π-M) and the lone pair of electrons on sulfur atom (σ-M) of thiophenes, with the coordinatively unsaturated sites (CUS) on Cu-BTC. Alkyl groups on 4- and/or 6-positions of thiophenic compounds function as both eletron donor to increase π-M interaction and steric inhibitor to decrease σ-M interaction. MOFs with strong and highly dense CUS can be promising materials for ADS of fuels.

In this work, an inexpensive and commercially available bentonite was modified by sulfuric acid and explored as the new type of support to immobilize tetraethylenepentamine (TEPA) for CO2 capture from flue gas. By applying sulfuric acid treatment, the textural properties, in particular, pore volume and surface area of bentonite, were significantly improved. Bentonite treated with 6 M sulfuric acid (Ben_H2SO4_6M) can reach a pore volume of 0.77 cc/g from that of the parent bentonite of 0.15 cc/g. With the maximum TEPA loading of 50 wt % onto the Ben_H2SO4_6M sorbent, the maximum CO2 breakthrough sorption capacity reached 130 mg of CO2/g of sorbent at 75 °C under a dry condition. With an addition of moisture to the simulated flue gas, the CO2 sorption capacity can be further improved to 190 mg of CO2 at 18 vol% of moisture addition sorbent due to the bicarbonate formation under a wet condition. The TEPA/Ben_H2SO4_6M sorbents show a good regenerability and thermal stability below 130 °C. The high CO2 sorption capacity, positive effect of moisture addition, and low capital cost of the raw bentonite materials imply that TEPA/Ben_H2SO4_6M could be a promising sorbent for cost-efficient CO2 capture from flue gas. The sulfuric acid treatment was demonstrated as an effective method for bentonite modification to immobilize TEPA for CO2 capture.

This work investigated the effect of surface functionalities of various unmodified and mildly modified carbon materials on the adsorption of water vapor at different relative humidity (RH) ranges. The adsorption isotherms of various carbon adsorbents were measured on a dynamic vapor sorption system. The carbon adsorbents were characterized by N2 adsorption test, scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX), Boehm titration, oxygen K-edge X-ray absorption near-edge structure (XANES) spectroscopy, temperature programmed desorption (TPD), and infrared (IR) spectroscopy. It is suggested that oxygen functional groups on the carbon surface play a critical role for water vapor adsorption. With the modification of carbon surface by (NH4)2S2O8 in H2SO4, −COOH, and S═O functional groups are introduced on the carbon surface. The surface functionalities, in particular −COOH and S═O functional groups on carbon surface, may govern the adsorption of water vapor at low RHs (RH < 40%); while the other types of oxygen functional groups, such as −OH, may contribute to the adsorption of water vapor at medium or high RHs. At high RHs (>70%), textural property, especially pore volume of carbon materials may govern the dehumidification capacity via pore filling mechanism, only if sufficient oxygen functional groups are present on carbon surface.

•Concerned with the question why ODS catalyst is not effective for real gasoline.•Reported the strong inhibiting effect of gasoline composition on ODS for the 1st time.•ODS reactivity is suggested to be determined by partial charge on S atom of thiophene.•Proposed approaches to improve ODS selectivity for real gasoline desulfurization.This work is concerned with the question of why oxidative desulfurization (ODS) catalyst that show good catalytic performance for ODS of model gasoline thiophenic compounds is not effective for real gasoline. For the first time, the effects of gasoline composition on ODS using a phosphotungstic acid/activated carbon (HPW/AC) catalyst with H2O2 were investigated. ODS of thiophene, one of the most difficult thiophenic compounds to be oxidized, was studied in a model fuel system, where a high thiophene conversion rate of 90% could be reached in 2 h at 90 °C. However, when applying the ODS to a real gasoline, the ODS conversion rate decreased to only 32%, suggesting a strong inhibiting effect of gasoline composition on ODS. The ODS studies in different model fuels suggested that the inhibiting effect can be ascribed to the competitive adsorption and oxidation with the presence of the alkenes and alkylated aromatic hydrocarbons in real gasoline. The active pi-electrons in alkenes and alkyl groups in alkylated aromatic hydrocarbons may react with polyoxoperoxo species or peroxo-metallate complexes formed by phosphotungstic acid–H2O2 interaction. Additionally, it was indicated that the ODS selectivity followed the order of benzothiophene > trimethylthiophene > dimethylthiophene ∼ methylthiophene > thiophene, suggesting the partial charge on the electron-rich sulfur atom may play a decisive role for its oxidation reactivity. To mitigate the inhibiting effect of gasoline composition on ODS, we propose (a) implementation of selective separation–oxidation processes; (b) choice of suitable selective oxidants; (c) optimization of selective ODS reaction temperature, etc. to improve ODS selectivity for real gasoline desulfurization applications.