New insights in single-step hydrodeoxygenation of glycerol to propylene by coupling rational catalyst design with systematic analysis

International audienceGlycerol-to-propylene routes involve overlapped hydrodeoxygenation (HDO) events on the active sites of heterogeneous catalysts which stability in aqueous media is a challenge. Herein, we proposed a rationalized approach to develop such catalysts by using hydrophobic-inert silica supports to protect highly reactive sub- 2 nm Mo particles against leaching and sintering. Propylene yield from 84.1% to 65.6% were obtained on MoOx nanoparticles at space-velocity ~1.7 h-1 and H2-pressure ~50 bar. Carburizing MoOx nanoparticles to β-Mo2C leads to an extremely efficient HDO catalyst, featuring, unprecedented TOF!"#!$%&'& ranging from ~153.1 h-1 to 226.4 h-1, while η-MoC phase gave better hydrogenation activity. Coupling in-situ XPS and kinetic data reveal that Mo5+, Mo3+ and Mo2+-C species play a critical role in the HDO events. Glycerol-to- propylene progresses over MoOx via successive Mo5+/Mo6+ and Mo3+/Mo4+ cycles, while over β-Mo2C/η- MoC, it occurs mostly on carbidic-oxycarbide surface. Surface accumulation of CxHyOz species caused Moδ+ re-oxidation, which hinders the HDO event

Bioglycerol-to-Propylene Routes: From Fundamental Catalysis to Process Design and Marketing

International audienceBioglycerol-to-propylene (GTP) routes are undergoing major developments in terms of both fundamental catalysis and process design on the way to becoming a connecting bridge between the biorefinery and polyolefin industries. This review starts introducing some GTP routes-related market potentialities and continues discussing significant mechanistic, kinetic, and engineering developments in GTP catalysis involving high-temperature, multistep, tandem, and single-step hydrodeoxygenation strategies. It highlights the main advances made in the design of efficient catalysts and in the elucidation of their active sites, thereby shedding light on state-of-the art preparation, functionalization, and characterization methods. The GTP mechanisms are also assessed over versatile metallic, acid, and bifunctional catalysts’ surfaces to discover which C–O bond is removed and which C=C bond is formed. GTP configurations are discussed as a function of the thermodynamic and operating conditions affecting catalysts’ reactivity, selectivity, and stability. They are also compared using various qualitative and quantitative criteria such as process configuration, severity of operating conditions, energy consumption, sustainability assessment, and propylene production. We thus intend to provide a broad overview of GTP catalysis for inducing new opportunities in the biorefinery-to-olefins field

New mechanistic insights into the role of water in the dehydration of ethanol into ethylene over ZSM-5 catalysts at low temperature

International audienceThe low-temperature dehydration of bioethanol-to-ethylene is of great interest to reduce energy consumption and achieve high product purities in the biorefinery and olefin industry. Thermokinetic constraints, however, lead to low ethylene selectivity at low temperature. In this work, we integrate a new approach that combines a hierarchical acid H-form ZSM-5 (HZSM-5) with systematic catalytic testing to study how the physicochemical modification of the surface and intermediate catalytic species affect the ethanol-to-ethylene route at 225 °C. Four HZSM-5 zeolites were treated with OH species under basic conditions (OH−) or solely with H2O. Kinetic evidence coupled to 27Al-nuclear magnetic resonance, NH3-temperature-programmed desorption and N2 adsorption, as well as density-functional theory calculations, correlate ethylene selectivity with the appearance of new extra-framework Al(V) and Al(VI) species, acting as Lewis acid-sites. The adopted approach allows us to experimentally unveil the cooperative effect between Brønsted- and Lewis-acid sites that seem to play a key role in ethylene formation from ethanol at low-temperature via (i) a primary route via ethanol dimerization on neighboring Brønsted-acid sites to diethylether, which subsequently cracked on Lewis-acid sites to ethylene; (ii) a secondary route via the direct ethanol dehydration on Brønsted-acid sites. Theoretical calculations support the proposed catalytic cycle. These new insights shed light on the mechanism of ethanol-to-ethylene at low temperature, and on how the precise control over the strength of acid-sites and their population in HZSM-5 affects catalysis. This work progresses towards more active and stable catalysts, advancing into more mature low-temperature technologies for the dehydration of bioethanol into sustainable ethylene

Unveiling the Efect of Temperature, H2-Atmosphere and Space-Velocity on One-Pot Hydeodeoxygenation of Bioglycerol to Sustainable Propylene

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