Morphology-Oriented ZrO2-Supported Vanadium Oxide for the NH3-SCR Process: Importance of Structural and Textural Properties

ZrO₂ supports, with diverse morphologies (hollow sphere, star, rod, mesoporous), were produced using hydrothermal and evaporation-induced self-assembly methods. Zirconia-supported vanadium oxide catalysts were prepared by wet impregnation and used for the low-temperature selective catalytic reduction (SCR) of NO with ammonia. Characterization of catalysts includes N₂ physisorption, elementary analysis, X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction by H₂, and temperature-programmed desorption of NH₃. Significant differences in terms of activity are measured. 3 wt % V₂O₅ supported on mesoporous ZrO₂ (V/MZ) presents excellent N₂ yields (>90%, in the 200-400 °C interval), with a wide operating temperature window (NO conversion > 95%, in the 225-425 °C interval), and less interesting performances were obtained when vanadium oxide is supported over stars, hollow spheres, and rods. Surface characterization showed a content of tetravalent vanadium ion, when supported, decreasing in the order of mesoporous > hollow sphere > star > rod. This order is in perfect agreement with the order of performance of the catalyst in the NH₃-SCR reaction. The impact of tetravalent ion's presence on the surface is confirmed by diffuse reflectance infrared Fourier transform spectroscopy analysis, Brønsted acid sites generated on the surface, and the V⁴⁺-OH species involved in the reaction. The production of more important nitrite species over the tetragonal supported vanadium oxide catalyst could be another reason for the excellent NH₃-SCR performance displayed by the V/MZ catalyst. When supported over monoclinic zirconia, like vanadium oxide over star-type morphology, the adsorbed NH₃ species (NH₄⁺ and coordinated NH₃) reacted with NO _x adsorption species (nitrate) to form ammonium nitrate. Ammonium nitrate can be decomposed to N₂ and N₂O (or NO₂). Thus, NO conversion curves and N₂ yield curves over tetragonal zirconia (MZ) at lower temperature were ahead of those over V/star ZrO₂ because of the higher V⁴⁺ surface content and more active B acid sites associated with an easy formation of the nitrito intermediate.

Catalyst design for biorefining

The quest for sustainable resources to meet the demands of a rapidly rising global population while mitigating the risks of rising CO2 emissions and associated climate change, represents a grand challenge for humanity. Biomass offers the most readily implemented and low-cost solution for sustainable transportation fuels, and the only non-petroleum route to organic molecules for the manufacture of bulk, fine and speciality chemicals and polymers. To be considered truly sustainable, biomass must be derived from resources which do not compete with agricultural land use for food production, or compromise the environment (e.g. via deforestation). Potential feedstocks include waste lignocellulosic or oil-based materials derived from plant or aquatic sources, with the so-called biorefinery concept offering the co-production of biofuels, platform chemicals and energy; analogous to today's petroleum refineries which deliver both high-volume/low-value (e.g. fuels and commodity chemicals) and low-volume/high-value (e.g. fine/speciality chemicals) products, thereby maximizing biomass valorization. This article addresses the challenges to catalytic biomass processing and highlights recent successes in the rational design of heterogeneous catalysts facilitated by advances in nanotechnology and the synthesis of templated porous materials, as well as the use of tailored catalyst surfaces to generate bifunctional solid acid/base materials or tune hydrophobicity.

ZrO2/SBA-15 as an efficient catalyst for the production of γ-valerolactone from biomass-derived levulinic acid in the vapour phase at atmospheric pressure

25 weight% ZrO₂/SBA-15 catalyst exhibits good activity in the catalytic transfer hydrogenation of levulinic acid under vapour phase conditions at atmospheric pressure.