Improvement of the catalytic activity of Ni/SiO2-C by the modification of the support and Zn addition: Bio-propylene glycol from glycerol

In previous studies, we prepared Ni catalysts supported on a silica-carbon composite which is selective for obtaining 1,2-propylene glycol (1,2-PG). In order to improve the activity levels of this catalyst, in the present work we propose to modify the catalyst formulation by means of two strategies: on the one hand, to modify the acidity of the catalyst through the functionalization of the carbon support and, on the other hand, to modify the metallic phase by the addition of Zn from a controlled preparation technique (Surface Organometallic Chemistry on Metals), which allows the selective addition of small amounts of modifier on the metallic particles. The functionalization of the SC support at 80 degrees C employing HNO3 at 60 wt% as oxidizing agent allowed increasing the number of surface acid sites that provide Lewis-type acidity without loss of specific surface area. The addition of 1.1-1.8 wt% of Zn (which corresponds to catalysts NiZn0.2/SC and NiZn0.32/SC) generates the formation of an active site composed of an alpha-NiZn alloy responsible for the increase in activity. When the addition of Zn is 2.8 wt% (which corresponds to catalyst NiZn0.5/SC), the generation of a new tetragonal phase of beta(1)-NiZn would cause the decrease of catalytic activity. These results indicate that the Zn addition has a more significant effect upon the activity and selectivity on the C-O bond cleavage reactions than the effect of the support acidity upon the dehydration activity.