Adsorption of C2 gases over CeO2-based catalysts: Synergism of cationic sites and anionic vacancies

The synthesis of novel and efficient catalysts for acetylene hydrogenation exhibiting high selectivity towards ethylene is important due to the presence of selective acetylene hydrogenation reaction in petrochemical processing. Since adsorption of C<inf>2</inf> gases constitutes the primary step in catalytic hydrogenation and governs the selectivity of the catalysts, we have explored the C<inf>2</inf>-adsorption potential of reducible CeO<inf>2</inf>-based systems. The adsorption of C<inf>2</inf>-gases over CeO<inf>2</inf>-based materials was assessed using experimental in situ spectroscopic techniques and in silico theoretical studies based on density functional theory. The effect of Pd²⁺ substitution on adsorption was studied. The addition of Pd²⁺-ions was found to enhance the adsorption of the gases. Theoretical calculations provided insights into the modes of adsorption, adsorption energetics and reactant-catalyst interactions. The role of the presence of cationic substitution and anionic vacancies in strengthening the adsorption of gases was established. Pd-substituted reduced CeO<inf>2</inf> showed activity for the adsorption of all C<inf>2</inf> gases. On the basis of the aforementioned experimental and theoretical observations, the catalysts were tested for acetylene hydrogenation, and Pd-substituted CeO<inf>2</inf> was found to be a good catalyst for the reaction with complete acetylene conversion observed below 100°C.