Effect of Si(IV) substitution on the stability of microporous ZnAPSO-44 solid acid catalysts: a combined XAS/XRD study

Selective hydrolysis of hemicellulose from wheat straw by a nanoscale solid acid catalyst

A nanoscale catalyst, solid acid SO4(2-)/Fe2O3 with both Lewis and Brønsted acidity was found to effectively hydrolyze hemicellulose while keeping cellulose and lignin inactive, and selective hydrolysis of hemicellulose from wheat straw by this catalyst was also confirmed. The factors that significantly affected hydrolysis process were investigated with response surface methodology, and the optimum conditions for time, temperature, and ratio of wheat straw to catalyst (w/w) were calculated to be 4.10h, 141.97°C, and 1.95:1, respectively. A maximum hemicellulose hydrolysis yield of 63.5% from wheat straw could be obtained under these conditions. In addition, the catalyst could be recycled six times with high activity remaining.

Time resolved in situ X-ray diffraction study of crystallisation processes of large pore nanoporous aluminophosphate materials

Time resolved high-resolution X-ray powder diffraction was utilized to obtain detailed changes in the crystal structure parameters during the hydrothermal crystallization process of the nanoporous aluminophosphate AlPO-5 (AFI) structure. This in situ study offered not only the influence of metal ions on the onset of crystallization and estimation of the activation energy of the process, but also allowed us to determine in detail the changes in lattice parameters during this process. More importantly the time-resolved study clearly showed the lattice expansion in the divalent metal ions substituted system right from the on-set of crystallization process, compared to the one without any dopant ions, which suggest that an amorphous or poorly crystalline network is formed prior to crystallization that contains the large divalent ions (compared to Al(iii), the substituting element), which is in agreement with the combined XAS/XRD study reported earlier. A mechanism based on this and the earlier study is suggested.

Tracking the structural changes in pure and heteroatom substituted aluminophosphate, AIPO-18, using synchrotron based X-ray diffraction techniques

We report the structural changes that occur during the thermal removal of organic template molecules that occlude the pores of small pore nanoporous zeolitic solids, AlPO-18, SAPO-18, CoAlPO-18, ZnAlPO-18 and CoSAPO-18. The calcination process is a necessary step in the formation of active catalysts. The studies performed using time-resolved High Resolution Powder Diffraction (HRPD) and High Energy X-ray Diffraction (HEXRD) techniques at various temperatures reveal that changes that take place are dependent on the type of heteroatom present in the nanoporous solids. While time-resolved HRPD shows clear changes in lattice parameters during the removal of physisorbed water molecules and subsequent removal of the organic template, HEXRD data show changes in various near neighbour distances in AlPO-18, SAPO-18, CoAlPO-18, CoSAPO-18 and ZnAlPO-18 during the calcination process. In particular HEXRD reveals the presence of water molecules coordinated to Al(III) ions in the as-synthesised materials. Upon removal of the template and water, these solids show contraction in the cell volume at elevated temperatures while first and second neighbour distances remained almost unchanged.

Interplay between size and crystal structure of molybdenum dioxide nanoparticles--synthesis, growth mechanism, and electrochemical performance

A detailed study is presented on the formation of MoO(2) nanoparticles from the dissolution of the precursor to the final rodlike product, with a focus on the exploration of the inorganic reaction occurring ahead of the nucleation step, and interplay between size and crystal structure of MoO(2). In situ X-ray absorption spectroscopy experiments show that the crystallization and the growth process of MoO(2) nanorods is initiated by rapid reduction of the MoO(2) Cl(2) precursor in benzyl alcohol and acetophenone. This reaction triggers the nucleation of 2 nm MoO(2) particles with spherical shape and hexagonal crystal structure. The transformation from spheres into rods emerges as a complex process driven by oriented attachment. High-resolution transmission electron microscopy and X-ray diffraction results provide evidence that the 2 nm particles first aggregate into 5-20 nm-large oriented assemblies. The increase in particle size induces the phase transition from hexagonal to the less symmetrical monoclinic crystal structure, and finally the transformation into rods. Is it shown that electrodes for lithium-ion batteries based on MoO(2) nanorods have a long-term cycling life. The specific discharge capacity even after 200 cycles at a discharge rate of 1 C is about 300 Ah kg(-1) .