Physicochemical properties of Pt-SO4/Al2O3 alkane oxidation catalysts

A series of sulfated alumina catalysts were synthesised by wet impregnation with sulfate-containing solutions. The degree of surface sulfation and corresponding surface acidity could be readily tuned by varying the molarity of impregnating solution. Strong acid treatments (>0.1 M) induced aluminium-sulfate crystallisation with a concomitant decrease in porosity and surface acidity. Platinum-doped sulfated aluminas showed enhanced activity towards methane, ethane and propane combustion. Activity scaled with the degree of accessible surface sulfate and platinum loading, however C-H bond scission appeared rate-limiting over both pure and presulfated aluminas. The magnitude of sulfate-promoted propane oxidation was greatest under heavily oxidising conditions (C3H6∶O2 > 1:20) but independent of Pt loading, confirming that support-mediated alkane activation is the dominant factor in the promotional mechanism.

In situ studies of structure-reactivity relations in biodiesel synthesis over nanocrystalline MgO

High temperature processing of solvothermally synthesised MgO nanoparticles promotes striking changes in their morphology, and surface chemical and electronic structure. As-prepared NanoMgO comprised ∼4 nm cubic periclase nanocrystals, interspersed within an amorphous Mg(OH)(OCH3) matrix. These crystallites appear predominantly (1 0 0) terminated, and the overall material exhibits carbonate and hydroxyl surface functionalities of predominantly weak/moderate base character. Heating promotes gradual crystallisation and growth of the MgO nanoparticles, and concomitant loss of Mg(OH)(OCH3). In situ DRIFTS confirms the residual precursor and surface carbonate begin to decompose above 300 °C, while in situ XPS shows these morphological changes are accompanied by the disappearance of surface hydroxyl/methoxide species and genesis of O- centres which enhance both the surface density and basicity of the resulting stepped and defective MgO nanocrystals. The catalytic performance in tributyrin transesterification with methanol is directly proportional to the density of strong surface base sites. © 2010 Elsevier B.V. All rights reserved.

Novel sol–gel preparation of (P2O5)0.4–(CaO)0.25–(Na2O)X–(TiO2)(0.35−X) bioresorbable glasses (X = 0.05, 0.1, and 0.15)

Quaternary phosphate-based glasses in the P2O5–CaO–Na2O–TiO2 system with a fixed P2O5 and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol–gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised sol–gel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), 31P nuclear magnetic resonance (31P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol–gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol–gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly six-fold coordination environment. The 31P NMR and FTIR results revealed that the glass structure consist of mainly Q1 and Q2 phosphate units and the Ti4+ cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing Na2O content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO2 content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol–gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed.

Niobic acid nanoparticle catalysts for the aqueous phase transformation of glucose and fructose to 5-hydroxymethylfurfural

A family of bulk and SBA-15 supported peroxo niobic acid sols were prepared by peptisation of niobic acid precipitates with H2O2 as heterogeneous catalysts for aqueous phase glucose and fructose conversion to 5-hydroxymethylfurfural (5-HMF). Niobic acid nanoparticles possess a high density of Brønsted and Lewis acid sites, conferring good activity towards glucose and fructose conversion, albeit with modest 5-HMF yields under mild reaction conditions (100 °C). Thermally-induced niobia crystallisation suppresses solid acidity and activity. Nanoparticulate niobic acid dispersed over SBA-15 exhibits pure Brønsted acidity and an enhanced Turnover Frequency for fructose dehydration.