Ti-Si composite oxide-supported cobalt catalysts for CO_2 hydrogenation

In the present work, different silica-based supported cobalt （Co） catalysts were synthesized and used for CO2 hydrogenation for methanation. Different supports, such as SSP, MCM-41, TiSSP and TiMCM were used to prepare Co catalysts with 20 wt% Co loading. The supports and catalysts were characterized by means of N2 physisorption, XRD, SEM/EDX, XPS, TPR and CO chemisorption. It is found that after calcination of catalysts, Ti is present in the form of anatase. The introduction of Ti plays important roles in the properties of Co catalysts by：（i） facilitating the reduction of Co oxides species which are strongly interacted with support, （ii） preventing the formation of silicate compounds, and （iii） inhibiting the RWGS reaction. Based on CO2 hydrogenation, the CoTiMCM catalyst exhibites the highest activity and stability.

POISONING OF ACTIVE SITES ON ZIEGLER-NATTA CATALYST FOR PROPYLENE POLYMERIZATION

The effects of poisoning materials on catalytic activity and isospecificity of the supported Ziegler-Natta catalyst were investigated.A minor amount of simple structure of Lewis base,i.e.,methanol,acetone,ethyl acetate,was introduced into the catalyst slurry for partial poisoning catalytic active centers.It was found that the variations in deactivation power were in the order of methanol>acetone>ethyl acetate.The kinetic investigation via stopped-flow polymerization showed that poisoning compounds cau...

Oxidative dehydrogenation of ethanol over Cu/Mg-Al catalyst derived from hydrotalcite:effect of ethanol concentration and reduction conditions

The copper-modified Mg-Al catalyst(Cu/Mg-Al)was synthesized using the incipient wetness impregnation of copper onto the Mg-Al hydrotalcite derived from co-precipitation method.The effects of copper on the characteristics of catalyst were obtained using several characterization techniques.We found that only copper(I)oxide(Cu O)species were obtained on the surface after calcination in air by X-ray Diffraction(XRD).However,the basicity of the base decreases slightly,while the density of the base increases due to the decrease in Brunauer-Emmett-Teller(BET)surface area.We carried out the catalytic activity of the Cu/Mg-Al catalyst in the continuous flow reactor through oxidative dehydrogenation of ethanol.We obtained that the copper enhances the catalytic activity in this reaction,and the ethanol conversion increases with increase in temperature,while the acetaldehyde selectivity decreases because of the decomposition of acetaldehyde to carbon dioxide.The highest acetaldehyde yield of 41.8%was at 350℃.Moreover,we studied the effects of the ethanol concentration by varying the ethanol feed concentrations(99.9%,75%,and 50%).The ethanol conversion decreases with a decrease in the ethanol concentration due to the high adsorption of water molecules on the catalyst surface.Thus,the negative effect decreases at higher reaction temperature(350–400℃).Furthermore,we investigated the effect of the reduction condition of catalyst by varying the reduction temperature(300 and 400℃).The reduction process affects the catalytic activity.The Cu/Mg-Al was comparatively stable for 10 h upon time-on-stream test.It is used as a promising catalyst in oxidative dehydrogenation of ethanol without any reduction step.

Synergistic Effects of the ZnCl_2-SiCl_4 Modified TiCl_4/MgCl_2/THF Catalytic System on Ethylene/1-Hexene and Ethylene/1-Octene Copolymerizations

The copolymerizations of ethylene with 1-hexene or 1-0ctene by using TiC14/MgCI2/THF catalysts modified with different metal halide additives （ZnCI2, SIC14, and the combined ZnC12-SiCl4） were investigated based on catalytic activity and copolymer properties. It was found that the catalyst modified with mixed ZnC12-SiC14 revealed the highest activities for both ethylene/1-hexene and ethylene/1-0ctene copolymerization. The increase in activities was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Based on the FTIR measurements, the characteristic C--O--C peaks of the catalysts modified with metal halide additives were slightly shifted to lower wavenumber when compared to the unmodified catalyst. This showed that the modified catalysts could generate more acid sites in the TiC14/MgC12/THF catalytic system leading to an increase in activities as well as comonomer insertion （as proven by IaC-NMR）. However, Lewis acid- modifications did not affect the microstructure of the copolymers obtained. By comparison on the properties of copolymers prepared with the unmodified catalyst, it was found that polymers with ZnC12 and/or SIC14 modification exhibited a slight decrease in melting temperature, crystallinity and density. It is suggested that these results were obtained based on the different amount of ct-olefins insertion, regardless of the types of Lewis acids and comonomer.