Insights into the nature of the active sites of pt-wox/al2o3 catalysts for glycerol hydrogenolysis into 1, 3-propanediol

The chemo-selective hydrogenolysis of secondary hydroxyls is an important reaction for the production of biomass-derived a, ¿-diols. This is the case for 1, 3-propanediol production from glycerol. Supported Pt-WOx materials are effective catalysts for this transformation, and their activity is often related to the tungsten surface density and Brönsted acidity, although there are discrepancies in this regard. In this work, a series of Pt-WOx/¿-Al2O3 catalysts were prepared by modifying the pH of the solutions used in the active metal impregnation step. The activity–structure relation-ships, together with the results from the addition of in situ titrants, i.e., 2, 6-di-tert-butyl-pyridine or pyridine, helped in elucidating the nature of the bifunctional active sites for the selective production of 1, 3-propanediol. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Insights into the Nature of the Active Sites of Pt-WOx/Al2O3 Catalysts for Glycerol Hydrogenolysis into 1,3-Propanediol

The chemo-selective hydrogenolysis of secondary hydroxyls is an important reaction for the production of biomass-derived α,ω-diols. This is the case for 1,3-propanediol production from glycerol. Supported Pt-WOx materials are effective catalysts for this transformation, and their activity is often related to the tungsten surface density and Brönsted acidity, although there are discrepancies in this regard. In this work, a series of Pt-WOx/γ-Al2O3 catalysts were prepared by modifying the pH of the solutions used in the active metal impregnation step. The activity–structure relationships, together with the results from the addition of in situ titrants, i.e., 2,6-di-tert-butyl-pyridine or pyridine, helped in elucidating the nature of the bifunctional active sites for the selective production of 1,3-propanediol.This work was supported by the University of the Basque Country (UPV/EHU), European Union, through the European Regional Development Fund (ERDF) (Spanish MICIN Project: RTI2018-094918-BC43), and the Basque Government (IT993-16). Clara Jarauta Cordoba acknowledges financial support from the Spanish Government (BES-2014-069165 and EEBB-I-18-13018)

Valorisation of Biowastes for the Production of Green Materials Using Chemical Methods

With crude oil reserves dwindling, the hunt for a sustainable alternative feedstock for fuels and materials for our society continues to expand. The biorefinery concept has enjoyed both a surge in popularity and also vocal opposition to the idea of diverting food-grade land and crops for this purpose. The idea of using the inevitable wastes arising from biomass processing, particularly farming and food production, is, therefore, gaining more attention as the feedstock for the biorefinery. For the three main components of biomass—carbohydrates, lipids, and proteins—there are long-established processes for using some of these by-products. However, the recent advances in chemical technologies are expanding both the feedstocks available for processing and the products that be obtained. Herein, this review presents some of the more recent developments in processing these molecules for green materials, as well as case studies that bring these technologies and materials together into final products for applied usage

Quantification of acidic sites of nanoscopic hydroxylated magnesium fluorides by FTIR and (15)N MAS NMR spectroscopy

Lewis and Brønsted sites were quantified in a series of weak acidic hydroxylated magnesium fluorides by Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance spectroscopy (NMR) with pyridine as probe molecule. Molar extinction coefficients, which are necessary for quantitative FTIR measurements, were calculated by an easy approach. It utilizes the fact that both signals, used for the quantification by FTIR, are caused by the same deformation vibration mode of pyridine. Comparison of quantitative FTIR experiments and quantification by NMR shows that concentrations of acidic sites determined by FTIR spectroscopy have to be interpreted with caution. Furthermore, it is shown that the transfer of molar extinction coefficients from one catalyst to another may lead to wrong results. Molar extinction coefficients and concentrations of acidic sites determined by FTIR spectroscopy are affected by grinding and probably the particle size of the sample. High temperature during FTIR experiments has further impact on the quantification results.Peer Reviewe

Dehydration of d-xylose to furfural using different supported niobia catalysts

Solid acids catalysts based on niobium oxide incorporated on different supports (commercial fumed silica and γ-Al2O3, MCM-41 and SBA-15 silicas) have been synthesized, characterized by using XRD, N2 sorption at −196 °C, XPS, Raman spectroscopy, NH3-TPD and pyridine adsorption coupled to FTIR spectroscopy, and tested for the dehydration of d-xylose to furfural. A monophasic water and biphasic water/toluene systems were compared, obtaining similar xylose dehydration activity but improving considerably the furfural selectivity when the toluene was employed as co-solvent. The γ-Al2O3 support enhanced apparently the secondary reactions, as can be inferred for the lower furfural selectivity of the Al-12Nb catalyst compared with the silica supported catalysts. The highest conversion and furfural selectivity after 24 h (84% and 93%, respectively) were found for the SBA-12Nb catalyst, at 160 °C in water/toluene. The niobia loading barely affected the xylose dehydration activity, but the catalyst with a 12 wt% showed higher furfural selectivity. Alternative N2-stripping technique was also studied, improving the furfural yield and product purity in the stripped stream.The authors are grateful to the Spanish Ministry of Economy and Competitiveness (CTQ-2012-38204-C03-02 and CTQ-2012-38204-C03-03), Junta de Andalucía (P09-FQM-5070) and FEDER funds for financial support.Peer Reviewe

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

Dehydration of xylose to furfural using a Lewis or Brönsted acid catalyst and N2 stripping

The activity of Lewis (Nb2O5) and Brönsted (Amberlyst 70) acid catalysts for the cyclodehydration of xylose to furfural was studied. The nature of the acidity resulted in significant changes in the reaction mechanism. Lewis acid sites promote the formation of xylulose, while Brönsted acid sites are required to further dehydrate the sugar to furfural. Amberlyst 70 in water/toluene at 175 °C showed lower activity but gave a higher furfural yield. Using N2 as the stripping agent considerably improved the furfural yield and product purity in the stripped stream. Catalyst stability was also studied.This work was supported by funds from the Spanish Ministerio de Economía y Competitividad (CTQ-2012-38204-C03-03 and ENE2009-12743-C04-03) and from the Gobierno Vasco (Programa de Formación de Personal Investigador del Departamento de Educación, Universidades e Investigación). The authors are also grateful to the Junta de Andalucía (P09-FQM-5070) for financial support.Peer Reviewe