An Oxidative Route for the Production of Methyl Methacrylate: A Study Over Iron Phosphate Catalysts

Abstract

An iron phosphate catalyst prepared using the ammonia gel method was supported on silica (CAT 1) and a commercial iron phosphate catalyst was supported on silica using the wet impregnation method (CAT 2). The XRD patterns of both the catalysts showed the presence of quartz-like iron phosphate and a tridymite like phase. In situ XRD under a reducing environment and TPR showed the formation of iron pyrophosphate for both the catalysts at 500 °C. The Mossbauer spectra of the catalysts were similar and showed the presence of the ferric ion only. NH3-TPD revealed the presence of Lewis and Bronsted acidic sites on both the catalysts. Oxidative dehydrogenation reactions of methyl iso-burate (MIB) were carried out using a continuous flow fixed bed reactor at contact times of 0.4 and 0.8 s. The conversion of MIB was marginally higher at a contact time of 0.8 s. CAT 2 gave an 11 % yield of methyl methacryalate (MMA) compared to 21 % over CAT 1 at a contact time of 0.8 s. The conversion of MIB increased with co-feeding water. A maximum conversion of MIB (82 %) was obtained at 400 °C, giving a yield of 20 % MMA at a contact time of 0.8 s over CAT 1. However, co-feeding water increased the hydrolysis reaction also, which increased the yield towards iso-butyric acid and methacrylic acid.