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The isomerization of glucose to fructose in the presence of Sn-containing zeolite BEA (beta polymorph A) was studied by periodic DFT calculations. Focus was placed on the nature of the active site and the reaction mechanism. The reactivities of the perfect lattice Sn(IV) site and the hydroxylated SnOH species are predicted to be similar. The isomerization activity of the latter can be enhanced by creating an extended silanol nest in its vicinity. Besides the increased Lewis acidity and coordination flexibility of the Sn center, the enhanced reactivity in this case is ascribed to the reaction environment that promotes activation of the confined sugar intermediates through hydrogen bonding. The resulting multidentate activation of the substrate favors the rate-determining hydrogen-shift reaction. These findings suggest the important role of defect lattice sites in Sn-BEA for catalytic glucose isomerization.

The increasing volume of sewage sludge from wastewater treatment facilities is becoming a prominent concern globally. The disposal of this sludge is particularly challenging and poses severe environmental hazards due to the high content of organic, toxic and heavy metal pollutants among its constituents. This study presents a simple review of four sewage to energy recovery routes (anaerobic digestion, combustion, pyrolysis and gasification) with emphasis on recent developments in research, as well as benefits and limitations of the technology for ensuring cost and environmentally viable sewage to energy pathway. This study focusses on the review of various commercially viable sludge conversion processes and technologies used for energy recovery from sewage sludge. This was done via in-depth process descriptions gathered from literatures and simplified schematic depiction of such energy recovery processes when utilised for sludge. Specifically, the impact of fuel properties and its effect on the recovery process were discussed to indicate the current challenges and recent scientific research undertaken to resolve these challenges and improve the operational, environmental and cost competitiveness of these technologies.

The siting of Ti, Sn, and Zr framework heteroatoms in zeolite BEA and the resulting Lewis acidity were systematically investigated by periodic density functional theory (DFT) calculations. Mono as well as double substitutions were considered. Substitution of Si by Ti, Sn, or Zr in the lattice of BEA zeolite is not random. For all substituted zeolites, the introduction of heteroatoms at the T2 crystallographic position is preferred. Water adsorption was used as a probe for Lewis acidity of lattice sites in these substituted zeolites. Although the Lewis acidity of Sn- and Zr-substituted BEA zeolites is generally quite similar, it is substantially higher than that of Ti–BEA. The Lewis acidity of substituted zeolites strongly depends on the crystallographic location of the heteroatoms. For those lattice sites that can be approached from two different directions, interaction with water will be favored from the more accessible direction. Stable structures containing double lattice substitutions at distances below 5.0 Å are found in Sn–BEA but not in Ti– or Zr–BEA. It is argued that substituted heteroatoms play an important role during the activation of reactants, with their ability to activate them depending on the type of heteroatom. The presence of paired lattice sites in Sn–BEA zeolite substantially enhances Lewis acidity of the zeolites, which clearly distinguishes Sn–BEA from its Ti- and Zr-substituted analogues.

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