Victor Teixeira da Silva

Molybdenum carbide nanoparticles within carbon nanotubes as superior catalysts for γ-valerolactone production via levulinic acid hydrogenation

We report here for the first time that supported molybdenum carbide is an efficient catalyst to selectively convert levulinic acid into γ-valerolactone in the aqueous phase. We have observed that the support plays a fundamental role in the activity and stability of molybdenum carbide that is stable when supported in carbon nanotubes but undergoes deactivation when supported on activated carbon. Particularly, when the carbide nanoparticles are positioned within the carbon nanotubes, conversion and selectivity values higher than 99 and 90%, respectively, were observed at 30 bar of H2 and 200 °C using a continuous-flow trickle-bed reactor. In a turnover frequency (TOF) basis, these values are similar to those obtained for a ruthenium catalyst evaluated under the same conditions.

Physical and chemical studies of tungsten carbide catalysts: effects of Ni promotion and sulphonated carbon

Ni promoted tungsten carbides have been shown to be an effective catalyst for cellulose conversion reaction. With the use of both in situ and ex situ techniques an investigation into the physical and chemical aspects of the Ni-promoted tungsten carbide catalyst supported on activated carbon either in pure form or functionalized with sulfuric acid was conducted. In situ XRD analysis performed during the carburization process showed that non-promoted samples formed a mixture of nanosized W2C, WC1−x and WC carbide phases. In the case of Ni promoted catalysts, in situ XRD, XANES, XPS and TEM analysis revealed that Ni aids in lowering the carburization temperature by 50 °C but also assisted in the deposition of polymeric carbon onto the catalyst surface which reduced cellulose conversion. However, the results indicate beneficial effects caused by the high carbon coverage by stopping the W2C to WC carbide phase transition. Thus, carburization of Ni promoted samples produced only W2C phase, which is stable up to 800 °C. The functionalization of activated-carbon with –SO3H not only increases the hydrolysis of cellulose but also lead to a greater dispersion of Ni over the catalyst. The resulting improvement in the interaction between Ni/W/C increases the cellulose transformation in a one-pot synthesis towards the production of ethylene glycol.

Stability of Transition‐metal Carbides in Liquid Phase Reactions Relevant for Biomass‐Based Conversion

Transition‐metal carbides have been employed for biobased conversions aiming to replace the rare noble metals. However, when reactions are in liquid phase, many authors have observed catalyst deactivation. The main routes of deactivation in liquid phase biobased conversions are coke deposition, crystallite growth, leaching and oxidation. This Minireview identifies and discusses the main trends between routes of deactivation and catalyst properties. The nature of the support can influence catalyst deactivation by coke deposition and leaching (role of acidity or electronic effects). Although carbon based supports seem to be a good choice for carbides in coke‐sensitive reactions, deactivation by leaching is facilitated. The crystallite size of the carbide is related to deactivation by oxidation, larger crystallites (10 nm) have a higher resistance to oxidation than smaller crystallites (< 2 nm).

Catalytic Upgrading of Fats and Vegetable Oils for the Production of Fuels

This chapter provides an overview of the catalytic conversion of triglycerides (vegetable oils and fats) into biofuels, with emphasis on studies and processes available in the open literature that address vegetable oils. Initially, the definition and composition of the most commonly used vegetable oils as a source of biofuels is presented, followed by a detailed analysis of the transformation of these oils into biofuels via the catalytic processes of cracking and hydrotreating The process of transesterification for the production of biodiesel is presented in brief, with references provided for further depth on this topic. Increased attention is given to the hydrotreatment of vegetable oils through the presentation and analysis of key papers published in the open literature, especially regarding the catalysts employed. Finally, prospects for future development are presented.

Promotion effects of Pd on tungsten carbide catalysts: physiochemical properties and cellulose conversion performance

A multi-functional catalyst, which is able to perform both retro-aldol reactions followed by hydrogenation, is required to convert cellulose into value-added ethylene glycol (EG) in a one-pot reaction. Herein, we show the results of a catalyst comprising Pd-promoted tungsten carbide supported on activated carbon. Pd acts to hinder carbon deposition onto the catalyst surface during the carburization process, through the inhibition of methane decomposition species on the catalyst surface. XPS and TEM analysis show a cleaner surface which improves the W/C ratio. The enhanced interaction between Pd and W2C, results in higher cellulose conversions, and higher ethylene glycol (EG) yields when compared to non-promoted or Ni promoted tungsten carbide catalysts reported elsewhere. XAS, HR-TEM and SI-XEDS analysis showed Pd nanoparticles are well dispersed on the surface and in contact with W2C. Despite higher carburization temperatures, Pd-promoted tungsten carbide catalysts enhance the catalytic properties of the one-pot cellulose conversion reaction towards EG production when compared to Ni-promoted catalysts under the same catalytic reaction conditions.