Gas-phase conversion of glycerol over mixed metal oxide catalysts
ABSTRACT A series of aluminophosphates (APO) catalysts with Ce, Cu, Cr, Fe, Mn, Mo, V, and W oxide loading at a constant ratio M: Al = 1: 10 and PO4: Al = 1: 12 were prepared and characterized by N2 physisorption, XRD and NH3-TPD. Gas-phase dehydration of glycerol to produce acrolein and acetol was investigated at 280°C in presence of water. Conversion
and product distribution depended on the intrinsic acidity and the type of transition metal oxide. Best selectivity to acrolein
(52–58%) was obtained for W- und Mo-APO catalysts. Cr-, Mn- and W- oxide containing catalysts enhanced the formation of phenol,
acetaldehyde and CO
. The catalysts containing V- and Fe-oxide promoted the formation of allyl alcohol. All catalysts showed long term stability,
which can be attributed to the redox ability of the metal oxides that enhances the removal of coke deposits. The investigated
catalyst a specially W-APO and Mo-APO can be recommended for further controlled trials on a pilot plant for selective conversion
of water solution of glycerol to acrolein and/or acetol.
Keywordstransition metal oxide–Al2O3-PO4
- SourceAvailable from: Bo-Qing Xu[Show abstract] [Hide abstract]
ABSTRACT: Synthesis of acrolein by catalytic gas-phase dehydration of biomass-derivate glycerol was studied over various solid catalysts with a wide range of acid–base properties. The catalyst acidity and basicity were measured, respectively, by n-butylamine and benzoic acid titration methods using Hammett indicators. The most effective acid strength for the selective dehydration of glycerol to form acrolein appeared between −8.2 ≤ H0 ≤ −3.0, with which acrolein was produced at a selectivity of 60–70 mol%. The catalysts having very strong acid sites (H0 ≤ −8.2) effected a lower acrolein selectivity (40–50 mol%) due to more severe coke deposition in the reaction. Solid acids holding medium strong and weak acid sites (−3.0 ≤ H0 ≤ +6.8) were found to be not selective for the acrolein production, the acrolein selectivity being less than 30 mol%. The mass specific catalytic rate for the acrolein production showed a general trend to increase with the fractional acidity at −8.2 ≤ H0 ≤ −3.0. The catalytic data also suggest that Brønsted acid sites were advantageous over Lewis acid sites in catalyzing the selective synthesis of acrolein from glycerol dehydration. Solid base catalysts were shown not to be effective for acrolein production.Green Chemistry 01/2007; 9(10). · 6.83 Impact Factor
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ABSTRACT: The catalytic properties of nanocrystalline HZSM-5 catalysts with high Si/Al molar ratio (ca. 65) were investigated in the gas phase dehydration of aqueous glycerol. Compared with bulk HZSM-5, the small-sized catalyst exhibits greatly enhanced catalytic performance in glycerol dehydration even with very high GHSV (=1438h−1). Catalysts with different Si/Al ratios were studied, but it is difficult to separate the influence of Si/Al ratio from that of particle size. However, by varying the proton exchange degree for one mother batch of zeolite, a series of HxNa1–xZSM-5 catalysts with same particle size and different Brønsted acid site densities was prepared. The catalytic results for this series of samples show that high density of Brønsted acid sites favors the production of acrolein. Based on these results, small-sized HZSM-5 with high aluminum content appears to be most promising for gas phase dehydration of glycerol.Journal of Catalysis - J CATAL. 01/2010; 269(1):71-79.
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ABSTRACT: Different silica-, alumina-, and aluminosilicate-supported heteropolyacid catalysts were prepared using phosphomolybdic acid H3PMo12O40⋅xH2O, phosphotungstic acid H3PW12O40⋅xH2O, silicotungstic acid H4SiW12O40⋅xH2O, and ammonium phosphomolybdate (NH4)3PMo12O40⋅xH2O as precursor compounds. The as-synthesised solids were characterised by nitrogen adsorption, XRD, TG/DTA, Raman spectroscopy, and TPD of ammonia. Silica-supported heteropolyacids are rather well crystallised, whereas alumina-supported samples are X-ray amorphous. Investigations using Raman spectroscopy of calcined samples and TG/DTA revealed that molybdenum-containing heteropolyacids tend to decompose partly close to 400 °C into molybdates and MoO3 whereas tungsten-containing samples are stable. This makes in particular tungsten-based materials interesting acid catalysts for the dehydration of glycerol in the gas phase. In particular, the influence of selected support materials, catalyst loading, and temperature on acrolein formation was studied at standardised reaction conditions (10% by weight of glycerol in water, 225–300 °C, modified contact time 0.15 kg h mol−1). Surprisingly, alumina is found to be superior to silica as support material with regard to catalyst activity and selectivity. Nevertheless, tungsten based heteropolyacids showed outstanding performance and stability. Acrolein was always the predominant product with maximum selectivity of 75% at complete conversion over silicotungstic acid supported over alumina and aluminosilicate.Journal of Catalysis - J CATAL. 01/2008; 258(1):71-82.