Nadine Essayem

Selective aqueous phase oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Pt/C catalysts: influence of the base and effect of bismuth promotion

5-Hydroxymethylfurfural (HMF) was quantitatively oxidized to 2,5-furandicarboxylic acid (FDCA) at 100 °C under 40 bar air in moderately basic aqueous solution in the presence of active carbon supported platinum and bismuth–platinum catalysts. The transformation of HMF into FDCA proceeded via the 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) and 2,5-diformylfuran (DFF) intermediates; both of these were very reactive and rapidly oxidized to 5-formylfurancarboxylic acid (FFCA), the subsequent oxidation of which was found to be the rate-limiting step. The preparation method of the platinum catalysts influenced the particle size of metallic platinum and modified the surface of the support, therefore determining the activity. The addition of a carbonate base (Na2CO3/HMF molar ratio = 2) led to faster overall conversion than bicarbonate (NaHCO3/HMF = 4) by maintaining an appropriate pH for the oxidation reaction. The ex situ or in situ addition of a bismuth promoter still accelerated the reaction; the highest activity was observed for a Bi/Pt molar ratio of ca. 0.2. Furthermore, the promoter helped to prevent some deactivation of the Pt catalyst upon recycling experiments. Quantitative conversion of HMF (0.1 M) and >99% yield of FDCA were achieved using a molar ratio of HMF to Pt of 100 and Na2CO3 as the homogeneous base in less than 2 h.

Non-catalyzed and Pt/γ-Al2O3-catalyzed hydrothermal cellulose dissolution–conversion: influence of the reaction parameters and analysis of the unreacted cellulose

Hydrothermal dissolution and/or conversion of cellulose Avicel® occurred at 190 °C under 5 MPa of H2 in the absence of catalyst. This reaction is temperature and time dependent. A dissolution–conversion ratio of 35% was obtained after 24 h of reaction and glucose and HMF were detected as monomeric products in a global yield of less than 5%, indicating that the majority of the products are composed of soluble oligo- and polysaccharides. The unreacted cellulose was analyzed using XRD, 13C solid state NMR, TGA-DTA and SEM and compared to the initial cellulose. We showed that although morphology changes occurred during the reaction, no modification of the crystallinity was observed and that hydrothermal treatment did not affect a specific part of the cellulose polymer. The presence of Pt/γ-Al2O3 increased the initial rate of dissolution–conversion significantly as well as the distribution of the monomeric products. Pt and H2 atmosphere were seen to increase the dissolution–conversion ratio however their role has not been yet well established.

Selective Aerobic Oxidation of 5-HMF into 2,5-Furandicarboxylic Acid with Pt Catalysts Supported on TiO2- and ZrO2-Based Supports

Pt catalysts prepared over different metallic oxide supports were investigated in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in alkaline aqueous solutions with air, to examine the combined effect of the support and base addition. The base (nature and amount) played a significant role in the degradation or oxidation of HMF. Increasing amounts of the weak NaHCO3 base improved significantly the overall catalytic activity of Pt/TiO2 and Pt/ZrO2 by accelerating the oxidation steps, especially for the aldehyde group. This was highlighted by a proposed kinetic model that gave very good concentration-time fittings. Moreover, the promotion of the catalyst with bismuth yielded a Ptuf8ffBi/TiO2 catalytic system with improved activity and stability. Y2 O3 uf8ff and La2 O3 uf8ffZrO2 -supported catalysts exhibited lower activity than Pt/ZrO2 , which suggests no cooperative effect of the weakly basic properties introduced and the homogeneous base. Quantitative oxidation of HMF (0.1u2009M) and high yields of FDCA (>99u2009%) were obtained in less than 5u2005h by using an HMF/Pt molar ratio of 100 and Na2 CO3 as a weak base over Ptuf8ffBi/TiO2 (Bi/Pt=0.22).

Effect of the addition of Sn to zirconia on the acidicproperties of the sulfated mixed oxide

Zirconium hydroxide, tin hydroxide and the mixed hydroxide of tin nand zirconium (1:9) have been prepared, sulfated with a 0.1 nMaqueous H n 2 nSO n 4 n solution and ncalcinated at 873 K. The chemical composition of these solids has been ncharacterized by chemical analysis, differential thermal analysis n(DTA), X-ray photoelectron spectroscopy (XPS) and energy dispersive nX-ray (EDX–) scanning transmission electron microscopy (STEM), nand their structural and textural properties have been studied by BET nsurface area and XRD techniques. The nature of the acid sites n(Bronsted or Lewis) was characterized by in nsitu IR study of pyridine adsorption and desorption and their namount was found to depend on the sulfate content. nCatalytic properties have been studied for the isomerization nreaction of n-butane to isobutane, in the 423 to 523 K range nand for propan-2-ol conversion, in the 373 to 473 K range. Addition of nSn to ZrO n 2 n (SnO n 2 n:ZrO n 2 n=1:9) led to a nsolid solution and enhanced slightly (ca. 30%) the weak acid nfeatures of ZrO n 2 n and removed the basic properties of pure nSnO n 2 n which was shown to convert propan-2-ol to acetone. nUpon sulfation of ZrO n 2 n, nSnO n 2 n–ZrO n 2 n[1:9] and SnO n 2 n, the nacidity of the oxides was sharply enhanced. nSO n 4 n n 2- n/SnO n 2 n, which was inactive for nthe isomerization reaction, was only 60% less active than nSO n 4 n n 2- n/ZrO n 2 n for propan-2-ol ndehydration. This shows that sulfation of SnO n 2 n generates nacid sites of moderate strength. The presence of only 10% of nSnO n 2 n in ZrO n 2 n decreased the reaction rates per nSO n 4 n n 2- n by a factor of six for the initial nn-butane isomerization reaction and by a factor of seven for nthe propan-2-ol dehydration to propene and diisopropyl ether. It is nsuggested that the presence of Sn decreases the electron acceptor nproperties of Zr and thus its acidity strength. Since the rate per nsulfated species of both reactions decreased in the same proportion, none may consider that on SO n 4 n n 2- n/ZrO n 2 n nand SO n 4 n n 2- n/SnO n 2 n–ZrO n 2 n nsamples there is no site of moderate strength able to dehydrate npropan-2-ol without isomerising n-butane.

Ammonia adsorption–desorption over the strongsolid acid catalystH3PW12O40 and itsCs+ and NH4+ saltsComparison with sulfated zirconia

Ammonia thermodesorption using a thermal conductivity ndetector does not allow an unambiguous study of the acidic nproperties of strong solid acids such as heteropolycompounds nand sulfated zirconia. As a matter of fact, these strong nacids release compounds other than NH n 3 n during TPD nexperiments which obviously involves side-reactions. nIn the present work, in order to circumvent the preceding nproblems, NH n 3 n adsorption and TPD experiments were nperformed using a dual mass spectrometry (MS)–TCD ndetection system. The equipment was applied to the ncharacterization of the acidic properties of porous nheteropolycompounds. nCs n x nH n 3-x nPW n 12 n nO n 40 n and n(NH n 4 n) n 2.8 nH n 0.2 nPW n 12 n nO n 40 n, by comparison with the parent acid nH n 3 nPW n 12 nO n 40 n and another nstrong solid acid, sulfated zirconia. nIt was observed that gaseous NH n 3 n reacted and nformed ionic species, leading to n(NH n 4 n) n 3 nPW n 12 nO n 40 n in nthe case of heteropolyacids (HPA) and probably n(NH n 4 n)HSO n 4 n in the case of sulfated nzirconia. Consequently, based on the amount of nNH n 3 n irreversibly adsorbed at 373 K the number of nacid sites has been deduced. For all HPA samples, TPD nprofiles of NH n 3 n appeared quite similar suggesting nthat the TPD curves were more connected to the stability of nthese ammonium salts rather than to the acid strength of the nsolid.

Cellulose conversion with tungstated-alumina-based catalysts: influence of the presence of platinum and mechanistic studies.

The performances of platinum supported on tungstated alumina (Pt/AlW) in the hydrothermal conversion of cellulose at 190u2009°C under H2 pressure were evaluated and compared to that of Pt-free tungstated alumina (AlW). We show that the presence of Pt significantly increased the extent of conversion and led to a different product distribution with the formation of acetol and propylene glycol as the main products and a global yield of up to 40u2009%. Based on previous reports, we propose the formation of pyruvaldehyde on the Lewis acid sites of the tungstated alumina as a key intermediate. Pyruvaldehyde can then be transformed to acetol and propylene glycol or lactic acid depending on the presence or absence of supported Pt.

Influence of the activation temperature on the metal accessibility in model three-way catalysts

Abstract The influence of the reduction temperature on the accessibility of the metallic surface was studied on model ceria-alumina supported platinum or rhodium catalysts. For a 0.5% Pt-Ce/Al solid, the H M values, deduced from hydrogen irreversible chemisorption, decrease deeply with Tr, the reduction temperature, from 60% at Tr = 300°C to 19% at Tr = 500°C. This can be attributed to strong interactions between ceria and platinum, since, the initial H2 chemisorption could be restored after reoxidation. The presence of BaSO4 in the support accelerates the loss of metallic area, because of sulfur poisoning of the platinum surface. For Tr = 300°C, the dispersion values were in agreement with those deduced from FTIR spectroscopy of adsorbed CO. In the case of rhodium, a 37% H/M dispersion was obtained, which did not change when Tr was increased from 300 to 500°C. For two industrial Pt-Rh three-way catalysts, the behaviour was found similar to that of platinum, the amount of chemisorbed hydrogen decreasing for Tr > 350°C. Thus, in the three-way catalysts characterization, the maximum metal accessibility is obtained after a reduction at 300°C.

High yield production of HMF from carbohydrates over silica–alumina composite catalysts

An efficient and selective production of 5-hydroxymethylfurfural (HMF) from carbohydrates is achieved in the presence of mesoporous AlSiO catalysts in a THF/H2O–NaCl biphasic system. These mesoporous AlSiO catalysts are prepared by a facile sol–gel method and have tunable acidity. Their acidic sites are characterized and quantified by NH3-TPD, microcalorimetry of NH3 adsorption and Py-FTIR, then correlated with the catalytic isomerization and dehydration of glucose to HMF. The detailed studies show that the AlSiO-20 catalyst with a Si/Al ratio of 18 is favorable for HMF production due to its inherently high surface area, high amounts of acid sites and a suitable Bronsted/Lewis acid ratio. Over the AlSiO-20 catalyst, an HMF yield of 63.1% is obtained at 160 °C for 1.5 h in the biphasic THF/H2O–NaCl medium with 10 wt% glucose in water. Further conducting the amplification experiment 30 times, the HMF yield still reaches 60.2% and the yield has no obvious decline after four catalytic cycles; this is the best result for an amplification experiment of HMF from glucose over a heterogeneous catalyst so far. After separation, HMF can be used for the production of 2,5-furandicarboxylic acid (FDCA) and as high as 95% FDCA yield is obtained over the Pt/C catalyst. Furthermore, the AlSiO catalyst demonstrates excellent activity in the conversion of disaccharides, polysaccharides and even lignocellulosic biomass, indicating it would be a promising catalyst for the conversion of glucose and glucose-based carbohydrates to HMF in industry applications.

A new green approach for the reduction of graphene oxide nanosheets using caffeine

A simple and green chemistry approach for the preparation of reduced graphene oxide nanosheets was successfully demonstrated through the reduction of graphene oxide (GO) using caffeine as the reductant. Without using toxic and harmful chemicals, this method is environmentally friendly and suitable for the large-scale production of graphene. The samples of GO, before and after reduction with caffeine have been characterized by X-ray diffraction, Raman, Fourier transform infrared, X-ray photoelectron spectroscopy, thermogravimetric analysis and transmission electron microscopy.

Synthesis of Cu–MxOy/Al2O3 (M = Fe, Zn, W or Sb) catalysts for the conversion of glycerol to acetol: effect of texture and acidity of the supports

The purpose of this work is to study the relationships between the copper oxide structure, specific surface area, acidity of MxOy/Al2O3 (M = Fe, Zn, W and Sb) supports and subsequently the catalytic proprieties of the solids. The samples were characterized by XRD, N2 adsorption/desorption isotherms and microcalorimetry of NH3 adsorption. The XRD results (after and before reaction) of the Fe and Zn-containing solids present the formation of a copper-modified alumina structure (high dispersion of Cu species with a strong interaction with the support); however, it is not observed a copper-modified phase for the catalysts composed of W and Sb, since it was identified the isolated CuO phase (a lower dispersion of Cu with a poor interaction with the support). N2 adsorption/desorption isotherms analysis shows that the copper-modified alumina samples are mesoporous materials and have a high surface area compared to the other catalysts, which did not presented a copper-modified phase. The catalytic tests ascribed that the presence of a copper-modified structure improves the activity, selectivity and mainly the stability for conversion of glycerol to acetol. W and Sb-based samples present low stability in glycerol transformation to acetol probably due to its acidity leading to formation of coke, blocking the active sites as a result of the low number of sites per area (low surface area) as well as the sintering of the copper phase. Thus, the results explain that the choice of metal elements in the solids composition affects its structural, textural, acidity proprieties and consequently the catalytic performance.