Effect of Modifiers On Zirconia-Based Catalysts for Isosynthesis

This work reports the characterization and performance of modified zirconia catalysts for synthesis of isobutene from syngas (isosynthesis). Several commercial catalysts employing a range of modifier species are considered here. The catalysts examined include tungstated zirconia (W-ZrO₂), sulfated zirconia-alumina (S-ZrO₂-Al₂O₃) and lanthanum zirconia (La-ZrO₂).  Addition of such modifiers to zirconia is known to have an effect on the physicochemical properties of the catalyst which in turn affects catalytic performance for isosynthesis. In this work, catalyst properties are characterized via a number of diagnostic techniques including N₂ physisorption, x-ray diffraction, and probe-molecule chemisorption. Isosynthesis activity is evaluated in a packed bed reactor configuration and the results are analyzed in terms of the physicochemical characteristics of the catalysts. Catalyst activity test results indicate that the species of the modifier has a strong effect on carbon monoxide conversion and selectivity to isobutene. The amount of CO conversion decreases in the order W-ZrO₂ > S-ZrO₂-Al₂O₃ > La-ZrO₂. Despite decreased CO conversions, the lanthanum-modified catalyst shows the highest selectivity to isobutene in the hydrocarbon products.