Study of the gas-phase glycerol oxidehydration on systems based on transition metals (Co, Fe, V) and aluminium phosphate

Abstract

The gas-phase glycerol (Gly) transformation in the presence of oxygen has been studied on cobalt oxide systems (10 and 20 wt% Co) supported on a synthetic mesoporous aluminium phosphate (AlPO4) calcined at 350 °C, as well as on a binary Co-Al phosphate with a Co content of 10 wt%. Synthetic binary phosphate of Al-M (M = Fe, V) have also been tested. The acidity (number and nature of acid sites) of the solids was determined by pyridine adsorption, whereas the reducibility was determined by H2 TPR. The propene oxidation was employed as a test reaction. The influence of the amount of oxidant agent and the reaction temperature on both the glycerol conversion and the yield to reaction products was studied. The formation of acrylic acid; acetic acid and carbon dioxide was favoured for values of O2/Gly ≥ 2 molar ratio and of temperatures beyond 250 °C. The Co oxide species in the supported systems that were the easiest to reduce (lower H2 desorption temperature) exhibited the highest activity to produce acrylic acid. The formation of acetic acid and carbon dioxide was also promoted, suggesting the participation of the acid sites in addition to redox sites. Among the metals investigated here, Co would form part of the required catalyst for the formation of acrylic acid from glycerol. Based on the identified products in this study, some possible reactions involved in the glycerol transformation into oxidized compounds, have been suggested.