The Effect of Preparation Method on Ni/Ce/Al Catalyst for High Temperature Water-Gas Shift Reaction

High temperature water gas shift (HT-WGS) is an important catalytic process connected with reforming process in hydrogen production. Ni/CeO2-Al2O3 (or Al2O3) catalysts were studied in this work on the effect of catalyst preparation method toward the physicochemical properties and the HT-WGS activity. Ni/CeO2-Al2O3 were prepared by sol-gel and impregnation methods whereas Ni/Al2O3 was prepared by impregnation method. The catalyst samples were characterized by XRD, H2-TPR and H2-TPD techniques. The catalytic activities of HT-WGS catalysts was demonstrated at 550°C, GHSV of 2x105 mLh-1gcat-1and steam-to-CO ratio of 3. Nickel was detected as a nickel aluminate phase in the calcined catalyst. Ni strongly interacted with support in the calcined catalyst prepared by sol-gel method. The strong metal-support interaction can be resisted by preparing catalyst via impregnation and CeO2 can promote the H2O dissociation in HT-WGS mechanism. The highest metal dispersion, largest metal surface area and greatest HT-WGS activity were consequently achieved by Ni/CeO2-Al2O3 prepared from impregnation method

Pore size effects on physicochemical properties of Fe-Co/K-Al2O3 catalysts and their catalytic activity in CO2 hydrogenation to light olefins

In this work, the hydrogenation of CO2 to light olefins has been studied over the Fe-Co/K-Al2 O3 catalysts, while focusing on the impact by the pore sizes of Al2 O3 supports including 6.2 nm (S-Al2 3 ), 49.7 nm (M-Al2 O3 ) and 152.3 nm (L-Al2 O3 ) on the structure and catalytic performance. The characterization results demonstrate that the pore sizes of the Al2 O3 supports play a vital role on the crystallite size of Fe2 O3 , the reducibility of Fe2 O3 and the adsorption-desorption of CO2 and H2 . The catalyst with the smallest pore size (CS-Al2 O3 ) allows the formation of a small Fe2 O3 crystallite size due to pore confinement effects, yielding a low active component (Fe) after reduction at 400 °C for 5 h. The catalysts with the larger pore sizes of 49.7 nm (CM-Al2 O3 ) and 152.3 nm (CL-Al2 O3 ) provide the larger Fe2 O3 crystallite sizes which require a longer reduction time for enhancing degree of reduction, resulting in a high metallic Fe content, leading to a high CO2 conversion and a high selectivity toward hydrocarbon. Eliminating diffusion limitation by increasing the pore sizes of Al2 O3 supports can suppress the hydrogenation of olefins to paraffins and thus the largest pore catalyst (CL-Al2 O3 ) gives the highest olefins to paraffins ratio of 6.82. Nevertheless, the CL-Al2 O3 also favors the formation of C5+ hydrocarbon. Therefore, the highest light olefins yield (14.38%) is achieved over the catalyst with appropriated pore size (CM-Al2 O3 )