Evaluation of Rh/CexTi1−xO2 catalysts for synthesis of oxygenates from syngas using XPS and TPR techniques

Abstract

Rh/CexTi1−xO2 catalysts have been investigated for the synthesis of ethanol from syngas. For this purpose various CexTi1−xO2 (x=0, 0.25, 0.5, 0.75, and 1) solid solution supports were synthesized using co-precipitation, which is an inexpensive and environmental friendly method. 2wt% Rh has been deposited over these supports by using wet impregnation method. We have evaluated these Rh catalysts for synthesis of ethanol from syngas at atmospheric pressure and 350psi. Among, the various catalysts, Rh supported on Ce0.75Ti0.25O2 catalyst exhibit better selectivity toward oxygenates compared to other catalysts. Interestingly, Ti rich samples exhibit higher selectivity toward hydrocarbons while Ce rich samples exhibit higher selectivity toward oxygenated products. The catalytic results at atmospheric pressure show that titania rich catalysts exhibit higher H2 conversion and ceria rich catalysts exhibit higher CO-conversion at 250°C at atmospheric pressure. Temperature programmed reduction measurements suggest that Rh promotes the cerium surface reduction. X-ray photoelectron measurements show that all the catalysts exhibit peaks due to Ce4+ and Ce3+ oxidations states in the Ce 3d spectra. O1s spectra of activated Rh/TiO2 and Rh/Ce0.5Ti0.5O2 catalysts show two peaks after reduction in hydrogen. One peak is due to the oxygen atoms from the individual oxides and the other peak is from the compound formation between Rh and the support. X-ray photoelectron measurements of activated catalysts also show that Rh/Ce0.5Ti0.5O2 catalyst exhibit higher Rh1+ ions on the surface compared to Rh/TiO2 and exhibits better selectivity toward oxygenated products.