Methylbenzenes are among the most important organic chemicals today and, among them, p-xylene deserves particular attention because of its production volume and its application in the manufacture of polyethylene terephthalate (PET). There is great interest in producing this commodity chemical more sustainably from biomass sources, particularly driven by manufacturers willing to produce more sustainable synthetic fibres and PET bottles for beverages. A renewable source for p-xylene would allow achieving this goal with minimal disruption to existing processes for PET production. Despite the fact that recently some routes to renewable p-xylene have been identified, there is no clear consensus on their feasibility or implications. We have critically reviewed the current state-of-the-art with focus on catalytic routes and possible outlook for commercialisation. Pathways to obtain p-xylene from a biomass-derived route include methanol-to-aromatics (MTA), ethanol dehydration, ethylene dimerization, furan cycloaddition or catalytic fast pyrolysis and hydrotreating of lignin. Some of the processes identified suggest near-future possibilities, but also more speculative or longer-term sources for synthesis of p-xylene are highlighted.

This critical review examines recent scientific and patent literature in the application of microwave reactors for catalytic transformation of biomass and biomass-derived molecules with a particular emphasis on heterogeneous catalysis. Several recent reports highlight dramatic reductions in reaction time and even superior selectivity when microwaves are used. However, there are still many controversies and unexplained effects in this area that deserve attention. We critically review the available sources attempting to establish trends and elucidate the actual status of this area of research. Additionally, where possible, we discuss the potential for scale-up and commercial utilization of microwaves and impediments that currently hold back their implementation. This critical review aims at highlighting the opportunity of combining catalysis with microwave technology for biomass conversion but also to stimulate the reader to generate future understanding of the influence of the microwaves in catalytic processes in general.

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We have found that the utilization of carbon nanotubes as support for ruthenium nanoparticles increases hydrogenation activity over 40 times in terms of turnover frequency (TOF) when compared to activated carbon in the transformation of hydroxymethylfurfural to dimethylfuran. Catalysts based on carbon nanotubes produced 83.5% yield of dimethylfuran (TOF 819.7 h −1 ) in under 1 h at 150 °C and less than 20 bar hydrogen pressure, whereas the activated carbon catalyst required more than 3 h to give an 80% yield of dimethylfuran (TOF 36 h −1 ). The superior accessibility of pores in carbon nanotubes, plus an electronic promotional effect in the carbon nanotubes, appear to be responsible for the superior activity of the catalysts supported on carbon nanotubes. The catalysts were synthesized by impregnation and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen physisorption, temperature-programmed reduction, electron microscopy and pulse CO chemisorption to propose the structure−activity relationships. This work highlights the importance of the support in hydrogenating reactions with ruthenium and the potential applicability of carbon nanotubes as supports for the hydrogenation of other bioderivatives.

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The selective production of p-xylene and other aromatics starting from sugars and bioderived ethylene offers great promise and can eliminate the need for separation of xylene isomers, as well as decreasing dependency on fossil resources and CO 2 emissions. Although the reaction is known, the microporosity of traditional commercial zeolites appears to be a limiting factor. In this work, we demonstrate for the first time that simply desilication of microporous commercial zeolites by a simple NaOH treatment can greatly enhance conversion and selectivity. The [4 + 2] Diels-Alder cycloaddition of 2,5-dimethylfuran with ethylene in a pressurised reactor was investigated using a series of H-ZSM-5 catalysts with SiO 2 /Al 2 O 3 ratios 30 and 80 with increasing pore size induced by desilication. X-ray diffraction, scanning electron microscopy, 27 Al magic-angle spinning nuclear magnetic resonance, temperature programmed desorption of ammonia, and nitrogen physisorption measurements were used to characterise the catalysts. The enhancement of conversion was observed for all desilicated samples compared to the untreated zeolite, and increases in temperature and ethylene pressure significantly improved both dimethylfuran conversion and selectivity to p-xylene due to the easier desorption from the zeolite's surface and the augmented cycloaddition rate, respectively. A compromise between acidity and mesoporosity was found to be the key to enhancing the activity and maximising the selectivity in the production of p-xylene from 2,5-dimethylfuran.

Green, inexpensive, and robust copper‐based heterogeneous catalysts achieve 100 % conversion and 99 % selectivity in the conversion of furfural to furfuryl alcohol when using cyclopentyl‐methyl ether as green solvent and microwave reactors at low H2 pressures and mild temperatures. The utilization of pressurized microwave reactors produces a 3–4 fold increase in conversion and an unexpected enhancement in selectivity as compared to the reaction carried out at the same conditions using conventional autoclave reactors. The enhancement in catalytic rate produced by microwave irradiation is temperature dependent. This work highlights that using microwave irradiation in the catalytic hydrogenation of biomass‐derived compounds is a very strong tool for biomass upgrade that offers immense potential in a large number of transformations where it could be a determining factor for commercial exploitation.