M.F. Neira d'Angelo

Carbon-coated ceramic membrane reactor for the production of hydrogen by aqueous-phase reforming of sorbitol

Hydrogen was produced by aqueous-phase reforming (APR) of sorbitol in a carbon-on-alumina tubular membrane reactor (4 nm pore size, 7 cm long, 3 mm internal diameter) that allows the hydrogen gas to permeate to the shell side, whereas the liquid remains in the tube side. The hydrophobic nature of the membrane serves to avoid water loss and to minimize the interaction between the ceramic support and water, thus reducing the risks of membrane degradation upon operation. The permeation of hydrogen is dominated by the diffusivity of the hydrogen in water. Thus, higher operation temperatures result in an increase of the flux of hydrogen. The differential pressure has a negative effect on the flux of hydrogen due to the presence of liquid in the larger pores. The membrane was suitable for use in APR, and yielded 2.5 times more hydrogen than a reference reactor (with no membrane). Removal of hydrogen through the membrane assists in the reaction by preventing its consumption in undesired reactions.

Epoxidation of propene using Au/TiO2: on the difference between H2 and CO as a co-reactant

The role of the reducing gas in the direct epoxidation of propene to propene oxide (PO) using O2 over a Au/TiO2 catalyst was studied through experiments and density functional theory calculations. It was found that PO can be obtained using both H2 and CO as co-reactants. The yield of PO was much lower with CO than that with H2. The role of the oxygen atoms of the titania support was studied by quantum-chemical investigations, which show that the mechanism involving CO as a co-reactant should proceed via surface oxygen vacancies, whereas with H2 the well-accepted pathway involving OOH is favored. Steady-state isotopic transient kinetic analysis experiments demonstrate that support oxygen atoms are involved in PO formation when CO is used as the co-reactant.

Direct epoxidation of propene on silylated Au–Ti catalysts: a study on silylation procedures and the effect on propane formation

Silylation was employed on an active Au/Ti–SiO2 catalyst, in order to enhance catalyst performance for the direct epoxidation of propene to propene oxide (PO) using H2 and O2. The effect of using different silylating agents and procedures on surface hydrophobicity and subsequently on catalytic activity was systematically investigated. The best performing catalysts were found to be those prepared by gas phase silylation after Au deposition, using hexamethyldisilazane (HMDS) and tetramethyldisilazane (TMDS) as silylating agents. The time of silylation was found to be critical for obtaining enhanced catalyst performance. An increase in the PO yield, selectivity and H2 efficiency was observed on silylation. Interestingly silylation also led to suppression of propene hydrogenation which is a major drawback of the process. The enhancement in catalytic performance is attributed to an increase in hydrophobicity and to blocking of unwanted Ti–OH sites that are potential sites for propane formation.