Effect of reduction temperature on Ru-Ir/ZnO catalyst for selective hydrogenation of crotonaldehyde

A Ru-Ir/ZnO catalyst with metal loadings of 3% Ru and 3% Ir was reduced at different temperatures (150 to 400 degrees C) and tested for vapor-phase selective hydrogenation of crotonaldehyde at 80 degrees C. It was found that with increasing reduction temperature, the crotonaldehyde conversion over the catalysts first increased and then decreased. A conversion of 93.5% and the selectivity to crotyl alcohol of 86.6% was observed after 10 h reaction on a Ru-Ir/ZnO catalyst reduced at 200 degrees C. Various characterizations such as X-ray photon spectroscopy (XPS) and ammonia temperature-programmed desorption (NH3-TPD) results demonstrated that moderate interaction between the C=O bond and the M-0 (M = Ru, Ir or Ru-Ir alloy) due to the proper charge density of M-0, and surface acidity of the catalysts played decisive roles in the enhanced activity and selectivity obtained on the catalyst. In addition, the deactivation of the catalyst was due to the carbon deposit (including organic compounds) on the catalyst surface, as evidenced by Raman spectroscopy and temperature-programmed oxidation over the spent catalyst. Also, the strong adsorption of CO on the catalyst surface generated by a decarbonylation reaction could be another reason for catalyst deactivation, as evidenced by a CO poisoning experiment. (C) 2014 Elsevier B.V. All rights reserved.