Ru(4+) ion in CeO(2) (Ce(0.95)Ru(0.05)O(2-delta)): A non-deactivating, non-platinum catalyst for water gas shift reaction

Hydrogen is a clean energy carrier and highest energy density fuel. Water gas shift (WGS) reaction is an important reaction to generate hydrogen from steam reforming of CO. A new WGS catalyst, Ce(1-x)Ru(x)O(2-delta) (0 <= x <= 0.1) was prepared by hydrothermal method using melamine as a complexing agent. The Catalyst does not require any pre-treatment. Among the several compositions prepared and tested, Ce(0.95)Ru(0.05)O(2-delta) (5% Ru(4+) ion substituted in CeO(2)) showed very high WGS activity in terms of high conversion rate (20.5 mu mol.g(-1).s(-1) at 275 degrees C) and low activation energy (12.1 kcal/mol). Over 99% conversion of CO to CO(2) by H(2)O is observed with 100% H(2) selectivity at >= 275 degrees C. In presence of externally fed CO(2) and H(2) also, complete conversion of CO to CO(2) was observed with 100% H(2) selectivity in the temperature range of 305-385 degrees C. Catalyst does not deactivate in long duration on/off WGS reaction cycle due to absence of surface carbon and carbonate formation and sintering of Ru. Due to highly acidic nature of Ru(4+) ion, surface carbonate formation is also inhibited. Sintering of noble metal (Ru) is avoided in this catalyst because Ru remains in Ru(4+) ionic state in the Ce(1-x)Ru(x)O(2-delta) catalyst.

Ce(0.67)Fe(0.33)O(2-delta) and Ce(0.65)Fe(0.33)Pt(0.02)O(2-delta): New water gas shift (WGS) catalysts

Ce(0.65)Fe(0.33)Pt(0.02)O(2-delta) and Ce(0.67)Fe(0.33)O(2-delta) have been synthesized by a new low temperature sonochemical method using diethylenetriamine as a complexing agent. Due to the substitution of Fe and Pt ions in CeO(2), lattice oxygen is activated in Ce(0.67)Fe(0.33)O(2-delta) and Ce(0.65)Fe(0.33)Pt(0.02)O(2-delta). Hydrogen uptake studies show strong reduction peaks at 125 C in Ce(0.65)Fe(0.33)Pt(0.02)O(2-delta) against a hydrogen uptake peak at 420 degrees C in Ce(0.67)Fe(0.33)O(2-delta). Fe substituted ceria, Ce(0.67)Fe(0.33)O(2-delta) itself acts as a catalyst for CO oxidation and water gas shift (WGS) reactions at moderate temperatures. The rate of CO conversion in WGS with Pt free Ce(0.65)Fe(0.33)O(2-delta) is 2.8 mu mol g(-1) s(-1) at 450 C and with Pt substituted Ce(0.65)Fe(0.33)Pt(0.02)O(2-delta) is 4.05 mu mol g(-1) s(-1) at 275 degrees C. Due to the synergistic interaction of the Pt ion with Ce and Fe ions in Ce(0.65)Fe(0.33)Pt(0.02)O(2-delta), the catalyst showed much higher activity for CO oxidation and WGS reactions compared to Ce(0.67)Fe(0.33)O(2-delta). A reverse WGS reaction does not occur over Ce(0.65)Fe(0.33)Pt(0.02)O(2-delta). The catalyst also does not deactivate even when operated for a long time. Nearly 100% conversion of CO to CO(2) with 100% H(2) selectivity is observed in WGS reactions even up to 550 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

Evidence of residual entropy in the cubic spinel Zn2TiO4

The standard free energies of formation of Zn2Ti04 and ZnTi03 have been determined in the temperature range 930° to i ioo'x from electromotive force measurements on reversible solid oxide galvanic cells;Ag-5at%znll I Pt, + CaO-Zr02 ZnO I II Ag-5at%Zn Y20r Th02 CaO-Zr02 + ,Pt Zn2Ti04+ ZnTi03 and II Ag-5at%Zn CaO-Zr02 + ,Pt ZnTi03+ Ti02 The values may be expressed by the equations,2ZnO (wurtz) + Ti02(rut) -> Zn2Ti04(sp), f:!:.Go = -750-2-46T (±75)cal;ZnO(wurtz) +Ti02(rut) -> ZnTi03(ilmen) ,f:!:.Co = -]600-0·]99T(±50)cal.Combination of the free energy values with the calorimetric heat of formation, and low-temperature and high-temperature heat capacity of Zn2Ti04 reported in literature, suggests a residual entropy of ],9 (±0·6) cal K-1 mol ? for the cubic spinel. Ideal mixing of Zn2+ and Ti4+ ions on the octahedral sites would result in a configurational contribution to the entropy of 2· 75 cal K-1 rnol ".The difference is indicative of short-range ordering of cations on octahedral sites.

Corrosion of 310 stainless steel in H2 H2O-H2S gas mixtures; studies at constant temperature and fixed oxygen potential

Corrosion of SAE 310 stainless steel in H2-H2O-H2S gas mixtures was studied at a constant temperature of 1150 K. Reactive gas mixtures were chosen to yield a constant oxygen potential of approximately 6 × 10-13 Nm-2 and sulfur potentials ranging from 0.19 × 10-2 Nm-2 to 33 × 10-2 Nm-2. The kinetics of corrosion were determined using a thermobalance, and the scales were analyzed using metallography, scanning electron microscopy, and energy dispersive X-ray analysis. Two corrosion regimes, which were dependent on sulfur potential, were identified. At high sulfur potentials (P S 2 ± 2.7 × 10-2 Nm-2) the corrosion rates were high, the kinetics obeyed a linear rate equation, and the scales consisted mainly of sulfide phases similar to those observed from pure sulfidation. At low sulfur potentials (P S 2 ± 0.19 × 10-2 Nm-2) the corrosion rates were low, the kinetics obeyed a parabolic rate equation, and scales consisted mainly of oxide phases. Thermochemical diagrams for the Fe-Cr-S-O, Fe-Ni-S-O, Cr-Ni-S-O, and Si-Cr-S-O systems were constructed, and the experimental results are discussed in relation to these diagrams. Based on this comparison, reasonable corrosion mechanisms were developed. At high sulfur potentials, oxide and sulfide phases initially nucleate as separate islands. Overgrowth of the oxide by the sulfide occurs and an exchange reaction governs the corrosion process. Preoxidation at low oxygen potentials and 1150 K is beneficial in suppressing sulfidation at high sulfur potentials.