S. Kanungo

Facile Synthesis of Catalytic AuPd Nanoparticles within Capillary Microreactors Using Polyelectrolyte Multilayers for the Direct Synthesis of H2O2

Microreactors present innovative solutions for problems pertaining to conventional reactors and therefore have seen successful application in several industrial processes. Yet, its application in heterogeneously catalyzed gas–liquid reactions has been challenging, mainly due to the lack of an easy and flexible methodology for catalyst incorporation inside these reactors. Herein, we report a facile technique for obtaining small (<2 nm) and well-distributed catalytic nanoparticles on the walls of silica-coated capillaries, that act as micro(channel) reactors. These particles are formed in situ on the reactor walls using polyelectrolyte multilayers (PEMs), built by layer-by-layer self-assembly. Manipulating the PEMs’ synthesis condition gives easy control over metal loading, without compromising on particle size. Both monometallic (Au and Pd) and bimetallic (AuPd) nanoparticles were successfully obtained using this technique. Finally, these catalytic microreactors were found to exhibit exceptional activity for the direct synthesis of hydrogen peroxide from H2 and O2.

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.