Shiju Raveendran

The Ti3AlC2 MAX Phase as an Efficient Catalyst for Oxidative Dehydrogenation of n-Butane

Dehydrogenation or oxidative dehydrogenation (ODH) of alkanes to produce alkenes directly from natural gas/shale gas is gaining in importance. Ti3AlC2, a MAX phase, which hitherto had not been used in catalysis, efficiently catalyzes the ODH of n-butane to butenes and butadiene, which are important intermediates for the synthesis of polymers and other compounds. The catalyst, which combines both metallic and ceramic properties, is stable for at least 30 h on stream, even at low O-2:butane ratios, without suffering from coking. This material has neither lattice oxygens nor noble metals, yet a unique combination of numerous defects and a thin surface Ti1-yAlyO2-y/2 layer that is rich in oxygen vacancies makes it an active catalyst. Given the large number of compositions available, MAX phases may find applications in several heterogeneously catalyzed reactions.

Highly Selective Oxidation of Ethyl Lactate to Ethyl Pyruvate Catalyzed by Mesoporous Vanadia-Titania

The direct oxidative dehydrogenation of lactates with molecular oxygen is a "greener" alternative for producing pyruvates. Here we report a one-pot synthesis of mesoporous vanadia-titania (VTN), acting as highly efficient and recyclable catalysts for the conversion of ethyl lactate to ethyl pyruvate. These VTN materials feature high surface areas, large pore volumes, and high densities of isolated vanadium species, which can expose the active sites and facilitate the mass transport. In comparison to homogeneous vanadium complexes and VOx/TiO2 prepared by impregnation, the meso-VTN catalysts showed superior activity, selectivity, and stability in the aerobic oxidation of ethyl lactate to ethyl pyruvate. We also studied the effect of various vanadium precursors, which revealed that the vanadium-induced phase transition of meso-VTN from anatase to rutile depends strongly on the vanadium precursor. NH4VO3 was found to be the optimal vanadium precursor, forming more monomeric vanadium species. V4+ as the major valence state was incorporated into the lattice of the NH4VO3-derived VTN material, yielding more V4+-O-Ti bonds in the anatase-dominant structure. In situ DRIFT spectroscopy and density functional theory calculations show that V4+-O-Ti bonds are responsible for the dissociation of ethyl lactate over VTN catalysts and for further activation of the deprotonation of beta-hydrogen. Molecular oxygen can replenish the surface oxygen to regenerate the V4+-O-Ti bonds.

Designing effective solid catalysts for biomass conversion: aerobic oxidation of ethyl lactate to ethyl pyruvate

The direct oxidative dehydrogenation of lactates with molecular oxygen is a promising route for producing bio-based pyruvates. But practical implementation of this route means high yields and mild conditions, which in turn require expensive noble-metal catalysts. Here we report a novel catalytic approach for efficient conversion of ethyl lactate to ethyl pyruvate. We show that vanadia supported on activated carbon acts synergistically with homogeneous pyridine-type additives, giving high conversion and selectivity. Control experiments and simulations show that the reaction follows a two-step pathway: first, the pyridine-lactate complex forms, followed by transfer to the vanadium active site where the oxidation occurs. Building on these results, we design a new solid catalyst where the vanadia sites are impregnated on a pyridine-rich carbonaceous support made from poly(4-vinylpyridine). This catalyst, made from abundant elements, combines the advantages of the homogeneous pyridine additive and the vanadia active site. This combination lowers the local mass-transfer barriers and improves the stability. The catalyst gives over 90% selectivity at 80% conversion at 130 degrees C and 1 atm oxygen, and can be reused at least five times without losing activity.