Low temperature synthesis of liquid hydrocarbons from syngas on composite catalysts of Pd-doped Cu-Cr-Zn mixed oxides and an H-ZSM-5 zeolite.

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Synthesis of liquid hydrocarbons from syngas was studied at relatively low temperatures, below 300°C, using bifunctional composite catalysts composed of low-temperature type methanol-synthesis catalysts of Pd-doped Cu-Cr-Zn mixed oxides and an H-ZSM-5 zeolite. As a source of Zn component of the methanol synthesis catalyst, freshly prepared Zn(OH)2 from Zn(NO3)2 was more suitable than a commercial ZnO powder for higher hydrocarbon yields. Oxidation and succesive reduction (O-R) treatments of the composite catalysts were carried out at 400°C and in the range of from 400 to 800°C. When the reduction temperature of O-R treatment was 600°C, the performance of the composite catalysts was appreciably improved. Syngas (H2/CO=2) was converted to hydrocarbons, dimethyl ether, and CO2 with selectivities of 44.1, 1.4, and 54.5%, respectively, at 35.8% CO conversion at 290°C, 20atm, and 6, 000 hourly space velocity. The space-time conversion of CO to liquid hydrocarbons (C4-C11) and the corresponding selectivity were 9.5mol/l•h and 61.4%, respectively. By lowering the H2/CO ratio of syngas from 2 to 1, the liquid hydrocarbon selectivity increased to 68.4% whereas the space-time conversion of CO to liquid hydrocarbon decreased.