Performance of RuSn catalysts supported on different oxides in the selective hydrogenation of dimethyl adipate

Dimethyl adipate was chosen to probe the behaviour of RuSn catalysts supported on different oxides, namely alumina, silica, ceria, niobia and titania on selective hydrogenation. The bimetallic catalysts were prepared by co-impregnation and characterised by Mössbauer spectroscopy. The reaction was carried out in a liquid phase semi-batch reactor at 255 °C and a hydrogen pressure of 50 bar. The addition of tin promoted the formation of 1,6-hexanediol on all Ru–Sn-based systems, confirming the catalysts surface modification. Amongst the studied catalysts, the RuSn/TiO2 was the most promising. The Mössbauer data allowed the conclusion that the oxidation state of tin as well as the tin–ruthenium and tin–support interactions are indeed rather different according to the support. The tin–support interaction appears to be more relevant with alumina; on titania, the metal–metal interaction seems to be favoured instead. The ionic tin forms, whether Sn4+ or Sn2+, were credited for conducting the reaction to the formation of diol. It is suggested that the structure of the RuSn sites created over these catalysts acts differently on the dimethyl adipate activation when compared to the selective hydrogenation of aldehydes, ketones or fatty acids.