Mg/Ga mixed-oxide catalysts for phenol methylation: Outstanding performance in 2,4,6-trimethylphenol synthesis with co-feeding of water

In this paper, we report on a new catalyst type based on Mg/Ga/O for the gas-phase methylation of phenol with the aim of obtaining the synthesis of 2,4,6-trimethylphenol. This catalyst showed an outstanding performance compared to similar catalysts reported in the literature, with high yield to the desired product. Reasons for this excellent performance were related to the high activity in methanol dehydrogenation to formaldehyde, which is the rate-limiting step in the multi-step (but one-pot) process, as well as to the moderate acidic features due to Ga sites, which enhanced the intramolecular rearrangement of O-alkylated compounds. The surprising role for co-fed steam, which greatly enhanced the selectivity to 2,4,6-trimethylphenol, was also investigated, combining reactivity experiments, in-situ FT-IR spectroscopy, and DFT calculations. It was found that the co-adsorption of water significantly affects the chemo-selectivity of the reaction, thus decreasing the formation of O-alkylated compounds in favour of the desired C-alkylated compounds. Reasons for catalyst deactivation were also studied.