ZNO-CR2O3-5 CATALYST WITH VERY-LOW ZN(ZSM)CR RATIO FOR THE TRANSFORMATION OF SYNTHESIS GAS TO HYDROCARBONS/

Three Zn-Cr mixed oxide plus ZSM-5 compound catalysts with different c ompositions covering a wide range of Zn/Cr atomic ratios (0.064 to 1.9 13), aimed at the direct conversion of synthesis gas into hydrocarbons , were tested under different experimental conditions: temperature ran ged from 356 to 410 degrees C, pressure from 3.60 to 4.49 MPa and spac e velocity from 0.2 to 3.0 mmol reactants/(g(cat) min). Reaction produ cts included carbon dioxide, water and hydrocarbons with methanol conv ersion (through which hydrocarbons are formed) being complete. The cat alyst with the least content of zinc gave the highest yields of liquid hydrocarbons (up to 74% of total hydrocarbons). Different crystalline phases (ZnO, ZnCr2O4 and Cr2O3) were found in the methanol synthesis component as a function of Zn/Cr ratio, The low Zn/Cr catalyst was cha racterized by X-ray diffraction, differential thermal analysis, nitrog en adsorption, temperature-pro rammed reduction, Infrared and X-ray ph otoelectron spectroscopy. The only phases observed in this catalyst we re ZnCr2O4 and Cr2O3. Calcination temperature had an influence in both physical and chemical catalyst properties. After calcination, Cr-VI a nd Cr-III species could be seen on the catalyst surface, but only Cr-I II species were observed after reaction or reduction. The evidences ga thered suggest that Cr2O3 is mainly responsible for methanol synthesis , while ZnCr2O4 contributes to increase the specific surface area of t he catalyst and influences gas product distributions, Compound catalys ts with the mixed oxide (Zn-Cr) as the methanol synthesis component sh owed to be more active than those with the individual (Cr or Zn) oxide s.