Radio-frequency H-2 plasma treatment of AuPd/TiO2 catalyst for selective hydrogenation of acetylene in excess ethylene

摘要

Supported Au catalysts modified by addition of small amount of Pd (Au/Pd atomic ratio = 14) are prepared by deposition-precipitation with NH3 (DP-NH3) followed by impregnation methods on TiO2. Low-pressure radio-frequency (RF) H-2 plasma treatment has been applied to AuPd/TiO2 for the selective hydrogenation of acetylene. Compared with conventional thermal reduction (AuPd-250), the acetylene conversion over plasma-treated catalyst (AuPd-P) has been improved significantly while the ethylene selectivity shows the opposite trend. With additional thermal reduction on the plasma-treated catalyst (AuPd-P250), the acetylene conversion is decreased and the ethylene selectivity is increased, however, they are still in between those of AuPd-P and AuPd-250. To understand the plasma effect, the catalysts are characterized by XPS, in situ FTIR spectra of CO adsorption and pulse H-2 chemisorption techniques. The high acetylene conversion of AuPd-P is ascribed to its large amount of surface Pd sites for acetylene adsorption, while its poor ethylene selectivity is due to the formation of contiguous Pd ensembles, which will cause the over hydrogenation of acetylene. The DTG results of the used catalyst indicate that the formation of green oil on or in the vicinity of Pd is suppressed over AuPd-P and AuPd-P250, and that is the reason why the plasma-treated samples are less deactivated than AuPd-250. Published by Elsevier B.V.