The development of catalytic materials, hydrothermally stable and selective to the desired products, is still a challenge. The aim of the present work is to prepare a nickel catalyst with a metal loading of 5 wt% Ni supported on a SiO 2-C composite, to be used in the liquid-phase glycerol hydrogenolysis reaction. The most active and selective catalyst to 1,2-propylene glycol (1,2-PG) was Ni/SC-095, which presented surface acidity fundamentally represented by the presence of carboxylic groups which promoted the CeO cleavage reactions of the glycerol primary carbon to produce acetol, and subsequently by hydrogenation to produce 1,2-PG. Concerning the selection of operating conditions, the influence of the most relevant variables of the process were analyzed, i.e., temperature (220-260°C), glycerol concentration (30-65%), and hydrogen partial pressure (0-4 MPa). The best result was obtained at 260°C with 30 wt% glycerol, 6 h on reaction and a hydrogen partial pressure of 2 MPa. Under these conditions, selectivities of 77% towards 1,2-PG and 3% to acetol were obtained, with 56% of conversion. It was demonstrated that there are no important structural changes through the characterization of the used samples. Both the SC-095 support and the Ni/SC-095 catalyst maintained their BET surface area. By XRD and TEM, there could be a slight increase in particle size, which would indicate good resistance to sintering against the severe hydrothermal conditions of this reaction.

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°C employing HNO 3 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 α-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 β 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 CeO bond cleavage reactions than the effect of the support acidity upon the dehydration activity.

This work studies 2 wt% Pt catalysts. The support is a SiO 2 -C composite whose main features are a high specific surface due to its mesoporosity, a higher thermal stability than the C support, and the absence of surface acid sites which could promote the dehydration reactions that produce coke precursors. The Pt/SiO 2 -C catalyst has very small metallic particles (d va ¼ 1.37 nm) that favor the CeC bond cleavage reactions which allow obtaining total gas conversion at 450 C. With this catalyst, it is possible to obtain high yields to H 2 , between 4 and 5, which indicates that the active sites promote the WGS reaction, even with glycerol concentrations of 30 and 50%. Pt/SiO 2 -C is a very stable catalyst since it loses only 10% of its initial activity after 66 h on stream and is resistant to sintering and coke deposition.