The quest for selective heterogeneous hydrogenation catalysts is state of the art research. We present a simple surface modification method for Pt/TiO 2 catalysts employing organic thiols for the liquid phase selective hydrogenation of 4-nitrostyrene. Our modified catalyst shows a 100% switch of selectivity to 4-aminostyrene at conversion levels close to 100%.

The three-phase hydrogenation of nitrobenzene catalysed by nanosized gold over titania was investigated in a slurry. Simultaneous in situ ATR-FTIR monitoring of the liquid phase and at the solid/liquid catalyst interface identified the species adsorbed on the catalyst and those in the liquid phase during the reaction. Nitrosobenzene was not detected analytically while the spectroscopic measurements strongly indicated phenylhydroxylamine as an intermediate reacting before desorbing from the catalyst surface. Under the same reaction conditions, azobenzene and hydrazobenzene were identified as intermediates during the hydrogenation of azoxybenzene to aniline. When nitrosobenzene or phenylhydroxylamine was alternately fed as reactant, azoxybenzene was produced via a disproportionation route. With the former, azoxybenzene was not further reduced by hydrogen because nitrosobenzene deactivated the catalyst. Combined with H(2) uptake, the spectroscopic measurements provided new insights into the reaction mechanism of the gold catalysed hydrogenation of nitrobenzene and an update of the corresponding kinetics.

The cerium oxidation state in ceria-doped Rh/Al 2 O 3 catalysts during the methane steam reforming (MSR) reaction was determined by in situ X-ray absorption spectroscopy and online mass spectrometry at 773 K. The catalysts were characterized by electron microscopy and X-ray diffraction. The oxidation states of rhodium and cerium during MSR are related. A total of 25% of Ce 4+ reduces to Ce 3+ under a CH 4 /H 2 O/He flow when the catalyst is active in MSR (773 K). A slight reoxidation occurs when the catalyst is sequentially exposed to steam diluted in helium at high temperatures, showing that only a small fraction of CeO 2−x may be involved in the water activation step by reoxidation. The main role of ceria during reaction, besides the activation of water, is to stabilize the structure of alumina by forming CeAlO 3 and to maintain the dispersion of rhodium. KEYWORDS: methane steam reforming, Rh/Al 2 O 3 catalysts, CeO 2 , Sm 2 O 3 , in situ X-ray absorption spectroscopy