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.

•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

In this study, nitrogen atoms are successfully introduced into the skeleton of reduced graphene oxide (rGO) by thermal treatment under an ammonia atmosphere. The activities of the catalysts are tested for anthracene hydrogenation, over which nearly complete anthracene conversion (99%) and high selectivity to the deeply hydrogenated products (around 50%) are achieved. The synergy of graphitic N and the sp2 CC structure can activate anthracene via π–π interactions. Moreover, the pyridinic N can facilitate hydrogen dissociative adsorption. The cooperation between anthracene activation and hydrogen dissociative adsorption results in different catalytic activities of the catalysts. Moreover, the catalysts also show better catalytic performance for the hydrogenation of other polyaromatic hydrocarbons.

In this study, nitrogen atoms are successfully introduced into the skeleton of reduced graphene oxide (rGO) by thermal treatment under an ammonia atmosphere. The activities of the catalysts are tested for anthracene hydrogenation, over which nearly complete anthracene conversion (99%) and high selectivity to the deeply hydrogenated products (around 50%) are achieved. The synergy of graphitic N and the sp2 CC structure can activate anthracene via π–π interactions. Moreover, the pyridinic N can facilitate hydrogen dissociative adsorption. The cooperation between anthracene activation and hydrogen dissociative adsorption results in different catalytic activities of the catalysts. Moreover, the catalysts also show better catalytic performance for the hydrogenation of other polyaromatic hydrocarbons.

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.

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.

•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

•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

In this study, nitrogen atoms are successfully introduced into the skeleton of reduced graphene oxide (rGO) by thermal treatment under an ammonia atmosphere. The activities of the catalysts are tested for anthracene hydrogenation, over which nearly complete anthracene conversion (99%) and high selectivity to the deeply hydrogenated products (around 50%) are achieved. The synergy of graphitic N and the sp2 CC structure can activate anthracene via π–π interactions. Moreover, the pyridinic N can facilitate hydrogen dissociative adsorption. The cooperation between anthracene activation and hydrogen dissociative adsorption results in different catalytic activities of the catalysts. Moreover, the catalysts also show better catalytic performance for the hydrogenation of other polyaromatic hydrocarbons.

In this study, nitrogen atoms are successfully introduced into the skeleton of reduced graphene oxide (rGO) by thermal treatment under an ammonia atmosphere. The activities of the catalysts are tested for anthracene hydrogenation, over which nearly complete anthracene conversion (99%) and high selectivity to the deeply hydrogenated products (around 50%) are achieved. The synergy of graphitic N and the sp2 CC structure can activate anthracene via π–π interactions. Moreover, the pyridinic N can facilitate hydrogen dissociative adsorption. The cooperation between anthracene activation and hydrogen dissociative adsorption results in different catalytic activities of the catalysts. Moreover, the catalysts also show better catalytic performance for the hydrogenation of other polyaromatic hydrocarbons.