Pd catalyst promoted by two metal oxides with different reducibilities: Properties and performance in the selective hydrogenation of acetylene

Abstract

La oxide is known to be the best promoter among reducible metal oxides for acetylene hydrogenation. However, it requires high-temperature reduction, which is not feasible in commercial processes. To maintain the enhanced catalytic performance by La oxide addition while lowering the reduction temperature for application in commercial process, we added Ti oxide as a second promoter, which has a higher reducibility than La oxide. The Ti oxide is added to the Pd surface, which has been partially covered by La oxide, and maintains the modified geometric and electronic structures of the Pd catalyst induced by the high-temperature-reduced La oxide even after low-temperature reduction, as confirmed by H2 chemisorption and X-ray photoelectron spectroscopy. Surprisingly, Ti oxide further modifies the electronic structure of Pd, even for low-temperature reduction, due to its high reducibility, leading to higher ethylene selectivity than when La oxide is used exclusively. We also confirmed that a similar additive effect also applies to other metal oxides, i.e., Nb2O5.