Chemical vapor deposition (DLI-CVD) and characterization of multiphasic molybdate-based catalysts for propene oxidation

Abstract

Production of acrolein via the partial oxidation of propylene on oxidic catalysts is of major industrial importance. High selectivity and yields are obtained in conventional, multi-tubular reactors using multi-element molybdate catalysts, whose performance has been substantially improved over the last fifty years. However, this process could be considerably enhanced by introducing safer and cleaner chemistry, as well as less energy intensive processes, through the improved management of heat transfer and better production control. This study describes an initial attempt at depositing an efficient, multi-element molybdate catalyst in the millimetric channels of a monolithic reactor by means of direct liquid injection-chemical vapor deposition (DLI-CVD). The catalyst was then tested for the oxidation of propene to acrolein. The results show that the DLI-CVD technique can be successfully applied to the simultaneous deposition of the catalyst's constituent elements, namely Bi, Mo, Fe and Co, which leads to the formation of a catalytic surface oxide layer containing the active phases needed for the propylene oxidation reaction. Although the catalytic properties of the coated milli-reactor are not as good as those obtained with an equivalent powdered catalyst, the results are encouraging, since a selectivity to acrolein as high as 68% was obtained at 350 °C.