Cellulose conversion to glycols over DUT-8(Ni) derived nickel-tungsten/carbons: selectivity tuning.

International audienceThere have been various studies on the transformation of cellulose to low carbon polyols (C2,3), ethylene glycol (EG), propylene glycol (PG) and glycerol (Gly), which are prevailing intermediates in the manufacture of plastics, pharmaceuticals, food additives, and cosmetics, etc. Cellulose conversion to diols mainly involves 3 types of reactions: cellulose hydrolysis, retro-aldol condensation, and hydrogenation. For the formation of 1,2-PG, the sugar isomerization reaction is also involved. Using activated carbon-supported tungsten carbide (W2C/AC) catalysts, Zhang et al. obtained an EG yield of 76 % starting from cellulose [1]. Besides being a cheap non-noble metal-derived phase, a noteworthy advantage of tungsten carbide over other tungsten species (oxides and metal) is the preferential formation of EG among other polyols due to its Pt-like catalytic behavior. Yang et al. prepared Ni-W/C nanofiber catalysts, in situ fabricated through the pyrolysis of Ni, W-containing metal-organic framework fibers. A large productivity varying from 15.3 to 70.8 molEG.h-1.gW-1 was reported, which is two orders of magnitude higher than previously reported Ni-W-based catalysts [2]. Interestingly Sun et al. [3] showed the impact of the Sn phase and valence on the catalytic properties of bimetallic systems supported on activated carbon. When powder of metallic Sn was used with Ni/AC, a Ni-Sn alloy formed which promoted retro-aldol cleavage and hydrogenation, finally favoring EG production (58 %). When SnO was used, the catalyst promoted glucose isomerization, leading preferentially to PG (32 %). The above studies inspired our current work. A series of W and Ni-containing metal-organic frameworks were constructed by one-pot assembly of DUT-8(Ni) MOF precursors and Na2WO4·2H2O. A subsequent pyrolysis of the W@ DUT-8(Ni) materials at 700 °C under nitrogen produced nickel-tungsten/carbon catalysts. The following nomenclature was adopted for the resulting materials: NiW-l-x-C-N2; where x (nW/nNi) was set at 0.06, 0.12, 0.3, and 0.43, respectively. Figure 1 displays the catalytic results of the as-synthesized materials in the cellulose hydrogenolysis at 245 °C in a reaction time of 1 hour. Both materials with low (NiW-l-0.06-C-N2) and high (NiW-l-0.3-C-N2) W content were selective to EG (17 %). A remarkable yield switch to PG (36 %) was obtained at an average W loading (NiW-l-0.12-C-N2). The highest EG molar yield (25 %) was obtained over NiW-l-0.43-C-N2

New insights on the catalytic reductive amination of hydroxyacetone amination over RUWXC/AC Catalyst

International audienceThe production of chemicals and liquid fuels from renewable and non-edible lignocellulosic biomass has been considered as a promising way to reduce our dependance to fossil resources as well as to reduce CO2 release. Especially, nitrogen-containing molecules, particularly primary amines, are broadly used for the synthesis of pharmaceuticals, polymers, surfactants, agrochemicals, and dyes[1]. Owing to the high O/C ratio (~1/1) in biomass feedstocks[2], the production of oxygenates from biomass is rather straightforward and has been largely studied. However, the further production of valuable nitrogen-containing products is far less evident due to the deficit of efficient amination strategies of oxygenates. One way is the amination of aldehydes and ketones to primary amines, employing ammonia as the nitrogen source[3]. Due to the development of biorefining, renewable aldehydes and ketones including glycolaldehyde, glyceraldehyde, hydroxyacetone, and aromatic compounds are nowadays available at large scales, opening new opportunities to produce nitrogen-containing compounds[4]. For example, Liang et al. reported the use of partly reduced Ru/ZrO2 for the reductive amination of different biomass-based aldehydes/ketones in aqueous ammonia[5]. Despite this encouraging development, effective heterogeneous catalytic systems that allow the amination reaction to take place under milder conditions (T < 100 °C, P < 50 bar, aqueous phase, and without additives) with high amines’ yields are still lacking. In particular, the production of large-market amino alcohols from hydroxyacetone hasn’t been reported so far.Herein, we report the preparation of a highly efficient and robust catalyst, RuWxC/AC, for the reductive amination of hydroxyacetone (Figure 1). By varying several process parameters including time, temperature, the nature of nitrogen source, and pressure, up to 60 mol.% amines’ yield has been obtained. The promoting effect of tungsten carbide nanoparticles has been particularly investigated. Finally, a kinetic study has been conducted and will be discussed

Investigating (pseudo)-heterogeneous Pd-catalysts for kraft lignin depolymerization under mild aqueous basic conditions

International audienceLignin is one of the main components of lignocellulosic biomass and corresponds to the first renewable source of aromatic compounds. It is obtained as a by-product in 100 million tons per year, mainly from the paper industry, from which only 2–3% is upgraded for chemistry purposes, with the rest being used as an energy source. The richness of the functional groups in lignin makes it an attractive precursor for a wide variety of aromatic compounds. With this aim, we investigated the Pd-catalyzed depolymerization of lignin under mild oxidizing conditions (air, 150 °C, and aqueous NaOH) producing oxygenated aromatic compounds, such as vanillin, vanillic acid, and acetovanillone. Palladium catalysts were implemented following different strategies, involving nanoparticles stabilized in water, and nanoparticles were supported on TiO2. Significant conversion of lignin was observed in all cases; however, depending on the catalyst nature and the synthetic methods, differences were observed in terms of selectivity in aromatic monomers, mainly vanillin. All these aspects are discussed in detail in this report, which also provides new insights into the role that Pd-catalysts can play for the lignin depolymerization mechanism