Tuning redox and chemical characteristics of Mo-based catalysts for bioenergy applications – The case of catalysts supported on TiO2 or ZrO2

Abstract

A series of MoO3-MoS2 catalysts supported on TiO2 or ZrO2 were synthesized and studied. The aim of this work is to understand the main aspects that influence the catalytic performance of Mo-based catalysts in bioenergy applications. We used two sulfidation temperatures for changing the Mo species in both supports. The catalysts were characterized by N2 physisorption, XRD, SEM, H2-TPR, Raman spectroscopy and XPS. We found important changes in the chemical species of Mo, S and O atoms present in the catalytic materials at 200 or 400 °C of sulfidation temperature. The materials were tested in the hydrodeoxygenation (HDO) of palmitic acid as a model compound of fatty acids. We found some structure-activity relationships of these materials. For instance, the promotion of mixtures of Mo6+, Mo5+ and Mo4+ species increased the catalytic activity for all the materials. MoO3/TiO2 catalyst exhibits higher activity than its counterpart supported on ZrO2. However, the sulfidation of these materials resulted in highly active catalysts, specially using ZrO2. Oxygen vacancies are formed for the catalysts supported on ZrO2 upon sulfidation. Molecular models were employed for a better understanding of the interaction between palmitic acid and the catalytic surfaces. We found that a combination of Mon+ species with S-containing compounds and oxygen vacancies in the catalytic materials is key to develop new highly active catalytic materials for HDO of fatty acids.