Optimizing the structure of supported Pd catalyst for direct oxidative esterification of methacrolein with methanol

• Supported Pd catalyst was used for direct oxidative esterification of methacrolein.
• The effect of influence factors on structure of supported Pd catalysts was studied.
• Promoters had great effect on the crystallite structure and catalytic performance.
• Different Pd precursors had different adsorption mechanisms on support.
• Reducing agent and temperature affected the crystallite size.

It is challenging to produce methyl methacrylate with high yield using direct oxidative esterification of methacrolein with methanol under oxygen atmosphere, and the key factor is the development of high-efficient and long-life supported Pd catalyst. In order to get the excellent catalyst, the effect of main influencing factors, such as promoters, supports, Pd precursors and reduction agents, on the catalyst structure and the catalytic performance were systematically studied. The results of the analysis indicated that the addition of promoters Pb to Pd crystallites catalyst, made the formation of new active bimetallic Pd3Pb crystallites, which could improve the catalytic activity; supports with different components and physico-chemical properties had great influence on the size of bimetallic Pd3Pb crystallites; different Pd precursors had different adsorption mechanisms on the support which affected the dispersion of Pd; reductant and reduction temperature affected the size of Pd3Pb crystallites. These studies are important clues for developing the new and cheap catalyst for this kind of direct oxidative esterification reactions.