(472g) Niau Single Atom Alloys for the Oxidative Coupling of Methacrolein with Methanol

Direct oxidative esterification of methacrolein with methanol is a more environmentally benign route for producing methyl methacrylate in comparison with the traditional acetone cyanohydrin method [1]. Since the early work of Haruta et al., in which, Au showed remarkable activity and selectivity when it was highly dispersed in the form of nanoparticles (<5 nm diam.), it has been studied for many other reactions with high selectivity towards the desired products [2]. Nanoporous Au has been examined in gas phase and UHV studies for the methacrolein – methanol coupling, and an excess of methanol (>90%) was found necessary for the effective cross-coupling [3]. In addition, Au nanoparticles deposited on basic supports has also been tested for the liquid phase coupling reaction, but the reaction mechanism has not been investigated in detail [4].

In the present work, we study Au and NiAu alloy catalysts where Au is either supported in nanoparticle form on an inert support, SiO­₂, or unsupported in nanoporous form for the liquid phase oxidative coupling of methacrolein with methanol. The formation of highly dilute Ni-Au alloys is followed by CO-DRIFTS. Catalytic performance tests in the liquid phase show that these catalysts have almost 100% selectivity towards methyl methacrylate and remarkable stability. Addition of Ni atoms on Au surface greatly improves its reactivity (conversion increases from ~5% on Au to ~25% on NiAu) while selectivity is maintained at the same levels as pure Au catalysts. Both Au and NiAu systems (either in nanoparticle or in nanoporous form) were found to have similar activation energies by kinetic measurements. This is an indication that Au is the active site in both the pure Au and the NiAu single atom alloy systems for this reaction. The promoting effect of Ni is also investigated by operando ATR-IR spectroscopy under reaction conditions. In addition, ATR-IR provides an insight into the reaction mechanism through identification of reaction intermediates-adsorbates on the catalytic surface. The catalyst structure and composition were also followed by ICP, XRD, HRTEM, SEM and XANES – EXAFS.

Acknowledgements: This material is based upon work supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis (IMASC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE- SC0012573.

Reference

1. Yamamatsu, T. Yamaguchi, K. Yokota, O. Nagano, M. Chono, A. Aoshima, Catal. Surv. Asia 2010, 14, 124-131
2. Haruta, N. Yamada, T. Kobayashi and S. Iijima, J. Catal. 1989, 115, 301-309
3. Karakalos, B. Zugic, K.J. Stowers, M.M Biener, J. Biener, C.M. Friend, R.J. Madix, Surf. Sci 2016, 652, 58-66
4. Suzuki, T. Yamaguchi, K. Matsushita, C. Iitsuka, J. Miura, T. Akaogi and H. Ishida, ACS Catal. 2013, 3, 1845-1849