Reaction Networks in Propane Ammoxidation to Acrylonitrile Over Orthorhombic Mo-V-Nb-Te-O Catalyst

We investigated propane ammoxidation to acrylonitrile over hydrothermal Mo-V-Nb-TeO catalyst containing the dominant M1 phase, recently proposed as active and selective in this selective ammoxidation reaction. The reaction kinetics was studied in a tubular quartz reactor at 600-700K operated in both differential and integral regimes at 5-60% propane conversion. The results obtained in this study were examined on the basis of two reaction networks involving propane transformation via (1) parallel routes to propylene, acrylonitrile and carbon oxides and (2) propylene as the reaction intermediate for acrylonitrile. The results obtained indicated only a slight preference for the reaction network involving the propylene intermediate, which may be explained on the basis of catalytic behavior of the M1 and M2 phases present in the hydrothermal Mo-V-Nb-Te-O catalyst. The dominant M1 phase was capable of catalyzing all of the above transformation steps, whereas the M2 impurity phase was only active in propylene ammoxidation to acrylonitrile. The contribution of the M2 phase to propylene ammoxidation is expected to be less significant at industrially relevant high propane conversions because of the improved ability of the M1 phase to covert propylene into acrylonitrile at longer residence times

Transmission Electron Microscopy Study of Ni Silicides Formed during Metal-Induced Silicon Growth

Polycrystalline silicon thin films grown on a Ni prelayer by the metal-induced growth (MIG) technique were studied by cross-sectional transmission electron microscopy and shown to possess a columnar structure. A Ni silicide transition region is formed due to the reaction between a fine-grained metallic Ni with atomic Si provided by the deposition source. This region exhibits a stratified structure as revealed by selected area diffraction patterns. The top layer is found to be a pure NiSi2 phase, which provides nucleation sites for the epitaxial Si growth. The bottom layer represents a mixture of several randomly oriented phases with a more Ni-rich composition. Co-existence of the above mentioned phases suggests that the silicide formation is controlled by the Ni-to-Si concentration ratio rather than temperature. No migration of the Ni silicide precipitates into the silicon film is observed. The formation mechanism of poly-Si on a Ni prelayer is discussed

Simultaneous Concentration of Dissolved Solids and Recovery of Clean Water from Acid Mine Drainage Employing Membrane Distillation

This study explored the techno-economic feasibility of using membrane distillation to recover clean water from acid mine drainage employing both renewable and nonrenewable energy sources. A microporous hydrophobic polypropylene membrane displaying 0.45 um pores exhibited the highest water flux during long-term testing under steady state continuous process conditions. Currently, natural gas and electricity are the most economical energy sources for the proposed membrane separation process to treat acid mine drainage. However, by 2030 renewable sources, and PV in particular, will become competitive with nonrenewable energy sources

Quantum Size Effect Silicon Structures via Molecularly Self-Assembled Hybrid Templates

A novel approach for the synthesis of advanced functional inorganic materials with atomic-scale control over the size of periodic features on the sub-30 nm scale is presented. The key innovative aspect of this technique is the direct,bottom-up formation of a two-dimensional periodic array of spatially separated nanostructures in a self-organized thin-film porous template. This thin-film template is fabricated via biologically inspired hierarchical self-assembly of organic surfactant molecules in the presence of inorganic charged silicate species. The removal of organic molecules from such an organic/inorganic hybrid system creates a periodic array of pore channels of ∼3-30 nm diameter inside the thin-film silica template. This porous template is employed as a shadow mask to directly grow various functional nanostructures inside the confined environment of the periodic pore arrays. In the present study, silicon nanostructures were grown inside the templates by both chemical and physical (sputtering) vapor deposition. The quantum size effect was clearly pronounced in the room temperature photoluminescence spectra of the samples prepared by sputtering from a Si target, which makes the approach highly promising for the fabrication of nanoscale optoelectronic devices

Better catalysts through microscopy: mesoscale M1/M2 intergrowth in molybdenum-vanadium based complex oxide catalysts for propane ammoxidation

In recent decades, catalysis research has transformed from the predominantly empirical field to one where it is possible to control the catalytic properties via characterization and modification of the atomic-scale active centers. Many phenomena in catalysis, such as synergistic effect, however, transcend the atomic scale and also require the knowledge and control of the mesoscale structure of the specimen to harness. In this paper, we use our discovery of atomic-scale epitaxial interfaces in molybdenum–vanadium based complex oxide catalysts systems (i.e., Mo–V–M–O, M = Ta, Te, Sb, Nb, etc.) to achieve control of the mesoscale structure of this complex mixture of very different active phases. We can now achieve true epitaxial intergrowth between the catalytically critical M1 and M2 phases in the system that are hypothesized to have synergistic interactions, and demonstrate that the resulting catalyst has improved selectivity in the initial studies. Finally, we highlight the crucial role atomic scale characterization and mesoscale structure control play in uncovering the complex underpinnings of the synergistic effect in catalysis

Removal of Mercury from Simulated Flue Gas Desulfurization Wastewater using Functionalized Silica

<p>We report highly promising results for Hg²⁺ removal from FGD wastewater to address new EPA effluent limitation guidelines (ELG). Their novelty stems from the use of realistic Hg concentrations in the presence of total dissolved solids typical for FGD wastewater. Although similar adsorbents were reported previously, they were studied at unrealistically high Hg concentrations in deionized water. We demonstrated that MPTMS-silica and MBT-silica can reduce Hg²⁺ below its maximum contaminant levels (MCLs) and ELGs independent of the concentration of major ions.</p