Changxi Miao

Effect of modifiers on the activity of a Cr2O3/Al2O3 catalyst in the dehydrogenation of ethylbenzene with CO2

Chromium oxide supported on alumina was modified with various transition metal oxides by an incipient wetness method. The effect of modifiers on the activity of 20% Cr2O3/Al2O3 catalyst in the dehydrogenation of EB with CO2 was investigated. The activity is enhanced for ceria and vanadia modified supported chromium oxide catalysts, whereas the activity is decreased for catalysts modified with cobalt, manganese, molybdenum and zinc oxides. Carbon monoxide was detected in the course of the reaction, suggesting that carbon dioxide, which is one of the most important greenhouse gases, could be utilized as a mild oxidant in the oxidative dehydrogenation of ethylbenzene to styrene over unmodified and modified Cr2O3/Al2O3 catalysts.

Oxidative dehydrogenation of ethane with CO2 over Cr supported on submicron ZSM-5 zeolite

Abstract A series of submicron ZSM-5-supported chromium oxide catalysts were prepared and characterized by XRD, N2 adsorption, 27Al MAS NMR, SEM, XPS, laser Raman spectroscopy and diffuse reflectance UV-Vis spectroscopy. The catalytic performance of these materials during ethane dehydrogenation in the presence of CO2 was investigated. The catalysts exhibited both high activity and stability, with an ethane conversion of ∼65% and ethylene yield of ∼49% without any obvious deactivation following 50 h. Characterization results show that the excellent catalytic performance results from the high degree of dispersion of CrOx species on the submicron ZSM-5 surface. Both a high Si/Al ratio and the use of the Na-form of the ZSM-5 support were found to favor CrOx dispersion. The promotional effect of CO2 on the dehydrogenation reaction was quite evident and can be attributed to the reverse water-gas shift reaction.

Ethylbenzene Dehydrogenation in the Presence of CO2 over MCF-Supported Vanadium Oxide Catalysts

A series of vanadia catalysts supported on mesocellular silica foam (MCF) with a V content ranging from 2% to 10% were studied with respect to their performance in the dehydrogenation of ethylbenzene (EB) to styrene in the presence of CO2. The structural and textural characterization of these catalysts was done using N2 adsorption, X-ray diffraction, and temperature-programmed reduction. These catalysts were found to be effective for the dehydrogenation reaction and the 6%V/MCF catalyst showed the highest activity. The MCF-supported vanadia catalysts exhibited far higher activity than their conventional V/MCM-41 counterparts, which can be attributed to the higher reducibility and better diffusion of reactants and products in the former catalysts. A higher conversion was obtained during EB dehydrogenation with CO2 than with N2. This is due to the oxidative dehydrogenation of EB with the help of oxygen that originates from CO2 as well as the coupling of EB simple dehydrogenation with the reverse water-gas shift reaction.

Preparation of Highly Active Cr2O3-SiO2 Catalyst by Sol-Gel Method for Ethylbenzene Dehydrogenation in the Presence of CO2

The Cr_2O_3-SiO ? catalyst was prepared by a sol-gel method. It displays two times higher catalytic activity for the dehydrogenation of ethylbenzene in the presence of CO_2 than the regular SiO_2-supported chromia catalyst.The higher amount of Cr 6+ present in the former catalyst accounts for its superior catalytic performance in the dehydrogenation reaction.

Ethylbenzene dehydrogenation to styrene in the presence of carbon dioxide over chromia-based catalysts

The dehydrogenation of ethylbenzene to styrene in the presence of carbon dioxide over chromia-based catalysts prepared in different ways was investigated. The 25% Cr2O3/Al2O3 supported catalyst and the 20% Cr2O3–SiO2 mixed oxide catalyst display the highest activities for the reaction. XRD characterization of the catalysts reveals that the activity depends on the amount of dispersed chromia species in the catalysts. A combination of XPS and TPR studies shows that both Cr6+ and Cr3+ species are present in the precalcined catalysts and the Cr6+ species are probably the precursors of the active sites of the catalysts with higher activity. Under the same reaction conditions, the supported chromia and chromia mixed oxide catalysts give better catalytic performance than Fe2O3/Al2O3 and V/MgO catalysts.

Catalytic decomposition of N2O over Rh/Zn–Al2O3 catalysts

Zn–Al2O3 supports were prepared by impregnating commercial γ-Al2O3 powders with different amounts of Zn(NO3)2, followed by calcination in air at 500 or 800 °C. Rh/Zn–Al2O3 catalysts were then prepared by impregnating Zn–Al2O3 supports with Rh(NO3)3 followed by calcination in air at 500 °C. The catalysts and/or supports were characterized by ICP-OES, XRD, N2 adsorption, Raman spectroscopy, TEM-EDX, XPS, CO2-TPD, H2-TPR, and O2-TPD, and the catalytic performance of supported Rh catalysts in N2O decomposition was tested. It is concluded that the support can be described as ZnO/Al2O3 (ZnO supported on Al2O3) when calcining Zn(NO3)2/Al2O3 at 500 °C, whereas ZnAl2O4 spinel forms on the Al2O3 surface at 800 °C. Rh/Zn–Al2O3 catalysts are much more active than Rh/Al2O3 and Rh/ZnO. The best catalyst (Rh/Zn–Al2O3-800 with 1 wt% Rh and 1 wt% Zn) has the smallest Rh2O3 particle size and can desorb O2 at lower temperature than other catalysts. Both factors may be important for achieving high activity in N2O decomposition.

Direct conversion of bio-ethanol to propylene in high yield over the composite of In2O3 and zeolite beta

A series of In2O3-beta composites with different contents of zeolite beta were prepared by the deposition–precipitation method, followed by calcination at 700 °C, and their catalytic performance in the conversion of ethanol to propylene (ETP) was investigated. The physicochemical properties of the as-synthesized materials were characterized by XRD, N2 adsorption, SEM, NH3-TPD, CO2-TPD and a probe reaction. The combination of In2O3 and zeolite beta improves the propylene yield significantly. The optimal result was observed for the composite with a beta content of 20–50%, which gave ca. 50% yield of propylene. The role of beta in the In2O3-beta composite catalyst is to promote the conversion of the intermediate of acetone to propylene via an additional reaction pathway, which accounts for the superior propylene yield of the In2O3-beta composite in comparison with In2O3 (ca. 32%). The proximity of these two components (In2O3 and zeolite beta) plays a crucial role in achieving a high yield of propylene for the ETP reaction.

Oxidative Dehydrogenation of 1-Butene to 1,3-Butadiene Using CO 2 over Cr-SiO 2 Catalysts Prepared by Sol-gel Method

Abstractseries of Cr-SiO2 catalysts with a Cr content(mass fraction) ranging from 0.5% to 9% was prepared by a sol-gel method. The catalysts were characterized by XRD, N2 adsorption, EDX elemental mapping, Raman spectroscopy, UV-Vis spectroscopy, XPS and H2-TPR, and their catalytic behavior in the dehydrogenation of 1-butene to 1,3-butadiene(BD) using CO2 as a soft oxidant was studied. The initial BD yield is well correlated with the amount of Cr6+ in the fresh catalysts. The highest BD yield of ca. 34% is achieved on the catalysts with 5%―9% Cr at 600 °C and weight hourly space velocity(WHSV) of 4.5 g·gcat-1·h-1. The promoting effect of CO2 on the BD yield was observed, which can be attributed to the reaction coupling between a simple dehydrogenation of 1-butene and the reverse water-gas shift reaction as well as regaining the oxidation state(lattice oxygen) of reduced Cr3+ species due to the mild oxidation ability of CO2. The Cr-SiO2 catalyst exhibits higher BD yield than the Cr catalyst supported on SBA-15, which is attributed to the higher amount of Cr6+present on the former catalyst.