Enhancement Of Reduction Rate Research Articles

Effect of stress on NiO reduction in solid oxide fuel cells: a new application of energy-resolved neutron imaging

Recently, two new phenomena linking stress field and reduction rates in anode-supported solid oxide fuel cells (SOFCs) have been demonstrated, so-called accelerated creep during reduction and reduction rate enhancement and nucleation due to stress (Frandsenet al., 2014). These complex phenomena are difficult to study and it is demonstrated here that energy-resolved neutron imaging is a feasible technique for combined mechanics–chemical composition studies of SOFC components, including commercially produced ones. Cermet anode supports, which prior to the measurements were reduced under varying conditions such as different temperatures, various times and different values of applied stress, have been measured. Thus, samples with different contents (and gradients) of Ni and NiO phases were investigated. The first Bragg edge transmission neutron measurements applied for the studies of the reduction progress in these samples were performed at two neutron beamline facilities (ISIS in the UK, Helmholtz Zentrum Berlin in Germany). The obtained results demonstrate the possibility to image and distinguish NiO and Ni phases within SOFC anode supports by energy-resolved neutron imaging and the potential of the neutron imaging method forin situstudies of reduction processes.

Enhancement of Oxyanion and Diatrizoate Reduction Kinetics Using Selected Azo Dyes on Pd-Based Catalysts

Azo dyes are widespread pollutants and potential cocontaminants for nitrate; we evaluated their effect on catalytic reduction of a suite of oxyanions, diatrizoate, and N-nitrosodimethylamine (NDMA). The azo dye methyl orange significantly enhanced (less than or equal to a factor of 5.24) the catalytic reduction kinetics of nitrate, nitrite, bromate, perchlorate, chlorate, and diatrizoate with several different Pd-based catalysts; NDMA reduction was not enhanced. Nitrate was selected as a probe contaminant, and a variety of azo dyes (methyl orange, methyl red, fast yellow AB, metanil yellow, acid orange 7, congo red, eriochrome black T, acid red 27, acid yellow 11, and acid yellow 17) were evaluated for their ability to enhance reduction. Hydrogenation energies of azo dyes were calculated using density functional theory and a volcano relationship between hydrogenation energies and reduction rate enhancement was observed. A kinetic model based on Brønsted-Evans-Polanyi (BEP) theory matched the volcano relationship and suggests sorbed azo dyes enhance reduction kinetics through hydrogen atom shuttling between reduced azo dyes (i.e., hydrazo dyes) and oxyanions or diatrizoate. This is the first research that has identified this synergetic effect, and it has implications for designing more efficient catalysts and reducing Pd costs in water treatment systems.

P H dependence of synchrotron x-ray induced electroless nickel deposition

We investigated the room temperature electroless nickel deposition on glass, induced by synchrotron x ray. By irradiating electrolytes with intense x ray the onset time for Ni reduction disappears at high electrolyte pH (>6.0) in sharp contrast with conventional electroless deposition. The time for Ni reduction in irradiated solution also decreases with increase in electrolyte pH. Consequently higher reduction rates in alkaline solutions (pH>8.0) raise the Ni nucleation density during deposition, as illustrated by homogeneous and complete coverage of the substrate by nanoparticles within a short period of 1 min. The enhancement in reduction rate is attributed to high redox efficiency of hydrated electrons produced by x ray as well as their redox potential enhancements under higher electrolyte pH conditions.

Studies on the reduction of iron oxide with hydrogen

Kinetic studies have been carried out on the hydrogen reduction of pure α-Fe 2O 3 doped with foreign metal oxides employing a sensitive micro-gravimetric technique. The results show that the reduction of pure Fe 2O 3 proceeds by a consecutive two-step mechanism via Fe 3O 4, the overall rate being controlled by the topochemical reduction of Fe 3O 4 while that of doped oxides and hematite ore takes place by a different mechanism involving the mixed ferrite formed. In addition, the reduction of pure Fe 2O 3 is catalysed by metal additives in the presence of water vapour. This enhancement in reduction rate is attributed to a “hydrogen spill-over” effect.