Stable Ni/Nb 2 O 5 catalyst for the hydrotreating of diphenyl ether produced Key challenge in the design of solid catalysts for the HDO of lignin streams identified Lewis acidity crucial to HDO also assists catalyst deactivation via coke formation Recommendations for the catalyst design for lignin hydrotreating put forward

Structural stability is a pivotal property required for Nb2O5 to be applied as a solid-acid catalyst in heterogeneous catalytic reactions. When combined with Ni, Nb2O5 produces cheap and active hydrogenation catalysts. Ni-Nb2O5 operates as a bifunctional catalyst and is being widely explored for various catalytic applications without, however, exploring its structural stability and its effects on catalytic activity and durability. Herein we studied two forms of niobia, one with nonuniform morphology and another comprising a nanorod morphology. Various selected Ni loadings were dispersed on the two supports via a deposition–precipitation method. Physical and chemical characterization revealed that morphological control in combination with a highly efficient Ni deposition method is key in producing a structurally stable Ni-Nb2O5 catalyst. High surface area and porosity as exhibited by the Nb2O5 nanorods, in the pseudohexagonal phase, combined with small, well-dispersed Ni particles, provide a structurally stable material up to 500 °C, with high acidity (Lewis and Brønsted acid sites). Moreover, the local and long-range order, characterized in situ (XANES and XRD), determined the temperature limits for the optimization of metallic Ni particles in relation to the Nb2O5 structure.

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A multi-functional catalyst, which is able to perform both retro-aldol reactions followed by hydrogenation, is required to convert cellulose into value-added chemicals such as ethylene glycol (EG) in a one-pot reaction.

Resumo O objetivo geral deste projeto é avaliar o desempenho de catalisadores de niquel suportados em óxido de nióbio na reação de hidrodesoxigenação (HDO) de anisol, uma molécula modelo do bio-óleo. As amostras de óxido de nióbio foram obtidas através da síntese hidrotérmica em diferentes temperaturas e volumes, tendo sido também avaliado o impacto da calcinação na fase cristalina formada. Foi utilizada a téncica de difração de raio X no estudo das fases cristalinas desse catalisador. Enquanto a temperatura de síntese e volume tiveram pouco impacto na fase formada, o aumento da temperatura de calcinação ao aumento de temperatura e transição de fase. Catalisadores com diferentes teores de níquel foram obtidos e avaliados na reação de HDO do anisol.

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Cellulose is the most abundant biopolymer in nature and has great potential to be processed and to sustainably produce biofuels and chemicals. The catalytic conversion is one of the most promising ways for processing cellulose. The separation between the products and the catalysts is an important step for the industry, which puts the heterogeneous catalysis in prime position as route of conversion due to the easiness of separation of product and catalyst. Hydrogenolysis is a processing way that promotes breaking CC bonds and the removal of oxygen atoms, leading to a variety of fuels and chemicals. The carbides of transition metals supported on activated carbon are effectives in breaking CC bonds, while palladium acts both in breaking CC bonds and in the hydrogenation steps. So, this work studied the structural and catalytic properties of catalysts of tungsten carbides supported on activated carbon and promoted with palladium. Catalysts W X C without promoter and 1 and 2% Pd were prepared and characterized. The N 2 physisorption measurements showed that a mixture of micro and mesopores forms the catalysts. The analysis of X-ray diffraction revealed the predominance of W 2 C phase in the catalysts promoted with Pd, while in the catalysts absent from Pd a mixture of carbide phases occurred. XPS measurements showed that the greater amount of Pd in the sample, it is more tungsten exposed on the surface. Then, the catalysts were applied in cellulose conversion reactions under hydrogen pressure. The conversion of cellulose was determined by gravimetry (mass balance) and thermogravimetry, and the products were identified and quantified by GC and HPLC. Yields around 40% for ethylene glycol were obtained, corresponding to 77% conversion of cellulose, in reactions performed at 220 °C and 120 min reaction time, with catalyst 2% PdW X C/C. Additionally, different substrates and catalysts were tested for understanding the conversion mechanism and the role of each component of the catalyst in the reaction route. Obtaining ethylene glycol from cellulose goes through hydrolysis of the polysaccharide into glucose monomers, retro-aldol reaction producing glycolaldehyde and hydrogenating to obtain ethylene glycol.

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