A systematic catalytic investigation of the sulfur dioxide oxidation reactivity of several binary (MxOy/TiO2) and ternary (V2O5/MxOy/TiO2) supported metal oxide catalysts was conducted. Raman spectroscopy characterization of the supported metal oxide catalysts revealed that the metal oxide components were essentially 100% dispersed as surface metal oxide species. Isolated fourfold coordinated metal oxide surface species are present for most oxides tested at low coverages, whereas at surface coverages approaching monolayer polymerized surface metal oxide species with sixfold coordination are present for some of the oxides. The sulfur dioxide oxidation turnover frequencies (SO2molecules converted per surface redox site per second) of the binary catalysts were all within an order of magnitude (V2O5/TiO2>Fe2O3/TiO2>Re2O7/TiO2∼CrO3/TiO2∼Nb2O5/TiO2>MoO3/TiO2∼WO3/TiO2). An exception was the K2O/TiO2catalyst system, which is inactive for sulfur dioxide oxidation under the chosen reaction conditions. With the exception of K2O, all of the surface metal oxide species present in the ternary catalysts (i.e., oxides of V, Fe, Re, Cr, Nb, Mo, and W) can undergo redox cycles and oxidize sulfur dioxide to sulfur trioxide. The turnover frequency for SO2oxidation over all of these catalysts is approximately the same at both low and high surface coverages, despite structural differences in the surface metal oxide overlayers. This indicates that the mechanism of sulfur dioxide oxidation is not sensitive to the coordination of the surface metal oxide species. A comparison of the activities of the ternary catalysts with the corresponding binary catalysts suggests that the surface vanadium oxide and the additive surface oxide redox sites act independently without synergistic interactions: the sum of the individual activities of the binary catalysts quantitatively correspond to the activity of the corresponding ternary catalyst. The V2O5/K2O/TiO2catalyst showed a dramatic reduction in catalytic activity in comparison to the unpromoted V2O5/TiO2catalyst. The ability of potassium oxide to significantly retard the redox potential of the surface vanadia species is primarily responsible for the lower catalytic reactivity.

The catalytic oxidation of sulfur dioxide to sulfur trioxide over several binary (MxOy/TiO2) and ternary (V2O5/MXOY/TiO2) supported metal oxide catalysts was systematically investigated. The supported metal oxide components were essentially 100% dispersed as surface metal oxide species, as confirmed by Raman spectroscopy characterization. The sulfur dioxide oxidation turnover frequencies of the binary catalysts were all within an order of magnitude (V2O5/TiO2>Fe2O3/TiO2>Re2O7/TiO2∼CrO3/TiO2∼Nb2O5/TiO2>MoO3/TiO2∼WO3/TiO2). An exception was the K2O/TiO2 catalysts, which is essentially inactive for sulfur dioxide oxidation. With the exception of K2O, all of the surface metal oxide species present in the ternary catalysts (i.e., oxides of V, Fe, Re, Cr, Nb, Mo and W) can undergo redox cycles and oxidize SO2 to SO3. The turnover frequency for sulfur dioxide oxidation over all of these catalysts is approximately the same at both low and high surface coverages. This indicates that the mechanism of sulfur dioxide oxidation is not sensitive to the coordination of the surface metal oxide species. A comparison of the activities of the ternary catalysts with the corresponding binary catalysts suggests that the surface vanadium oxide and the additive surface metal oxide redox sites act independently without synergistic interactions. The V2O5/K2O/TiO2 catalyst showed a dramatic reduction in the catalytic activity in comparison to the unpromoted V2O5/TiO2 catalyst. The ability of K2O to significantly retard the redox potential of the surface vanadia species is primarily responsible for the lower catalytic activity of the ternary catalytic system. The fundamental insights generated from this research can potentially assist in the molecular design of the air pollution control catalysts: (1) the development of catalysts for low temperature oxidation of SO2 to SO3 during sulfuric acid manufacture (2) the design of efficient SCR DeNOx catalysts with minimal SO2 oxidation activity and (3) improvements in additives for the simultaneous oxidation/sorption of sulfur oxides in petroleum refinery operations.

The oxidation of sulfur dioxide to sulfur trioxide over supported vanadium oxide catalysts occurs as both a primary and secondary reaction in many industrial processes, e.g., the manufacture of sulfuric acid, the selective catalytic reduction of NO, with ammonia and the regeneration of petroleum refinery cracking catalysts. This paper discusses the fundamental information currently available concerning the molecular structure and sulfur dioxide oxidation reactivity of surface vanadia species on oxide supports. Comparison of the molecular structure and reactivity information provides new fundamental insights on the following topics related to the catalytic properties of surface vanadia species during the sulfur dioxide oxidation reaction:1. role of terminal V=O, bridging V-O-V and bridging V-O-support bonds,2. number of surface vanadia sites required to perform SO2 oxidation,3. influence of metal oxide additives,4. generation and influence of the surface sulfate overlayer,5. effect of surface acidity on the reaction turnover frequency,6. competitive adsorption between SO2 and SO3 and7. reaction kinetics.(C) 1999 Elsevier Science B.V. All rights reserved.

The objectives of this research are to establish the fundamental kinetics and mechanism of sulfur dioxide oxidation over supported vanadia catalysts and use these insights to facilitate the design of SCR DeNO(x) catalysts with minimal sulfur dioxide oxidation activity. A series of supported vanadia catalysts were prepared on various metal-oxide supports: ceria, zirconia, titania, alumina and silica. Raman spectroscopy was used to determine the coordination of surface species. At low vanadia loadings, vanadia preferentially exists on oxide support surfaces as isolated tetrahedrally coordinated (M-O)(3)V+5=O species. At higher vanadia loadings, the isolated (M-O)(3)V+5=O species polymerize on the oxide support surface breaking two V-O-M bonds and forming two V-O-V bridging bonds.The turnover frequency for sulfur dioxide oxidation was very low, 10(-4) to 10(-6) s(-1) at 400 degrees C, and was independent of vanadia coverage suggesting that only one vanadia site is required for the oxidation reaction. As the support was varied, sulfur dioxide oxidation activity of the supported vanadia catalysts varied by one order of magnitude (Ce>Zr, Ti>Al>Si). The basicity of the bridging V-O-M oxygen appears to be responsible for influencing the adsorption and subsequent oxidation of the acidic sulfur dioxide molecule. Over the range of conditions studied, the rate of sulfur dioxide oxidation is zero-order in oxygen, first-order in sulfur dioxide and inhibited by sulfur trioxide.The turnover frequency for sulfur dioxide oxidation over WO3/TiO2 was an older of magnitude lower than that found for V2O5/TiO2, and no redox synergism between the surface vanadia and tungsten oxide species was evident for a ternary V2O5/WO3/TiO2 catalyst. This suggests that WO3 promoted catalysts may be suitable for low-temperature SCR where minimal sulfur dioxide oxidation activity is required. (C) 1998 Elsevier Science B.V. All rights reserved.

The interactions between surface sulfate and surface vanadate species present on sulfated supported vanadia catalysts under dehydrated conditions have been investigated with infrared and Raman spectroscopies. The surface sulfate species present on sulfated TiO2, ZrO2, and Al2O3 supports and V2O5/TiO2, V2O5/ZrO2, and V2O5/Al2O3 catalysts have identical molecular structures, i.e., (M-O)(3)S=O, where M = Ti, Zr, or Al. Interactions between the surface vanadia and surface sulfate species do not lead to the formation of sulfate-vanadate compounds. The surface sulfate species on the V2O5/TiO2 V2O5/ZrO2, and V2O5/Al2O3 catalysts anchor to and displace only the most basic support hydroxyls, while the surface vanadate species titrate both basic and neutral support hydroxyls forming a complete close-packed monolayer. At low V2O5 loadings, the surface vanadia species on these catalysts preferentially titrate basic hydroxyls, which consumes the sites capable of sulfate adsorption. Thus, the amount of adsorbed surface sulfate species decreases in an exponential fashion with increasing surface coverage of the vanadia species. Strong interactions between sulfate species and CeO2 lead to the formation of bulklike cerium-oxy-sulfur compounds. The stable monolayer of VO4 units present on the surface of a 4% V2O5/CeO2 catalyst was disrupted upon sulfation and lead to the formation of bulklike cerium sulfate and cerium vanadate compounds.

A bench-scale system to continuously separate and concentrate SO2 from flue gas has been developed and tested. The separation is accomplished due to the relative adsorption strengths of SO2 and water on a synthetic mordenite, a phenomenon known as rollup. The continuous concentration system (CCS) is comprised of two pairs of packed beds that cycle between cleaning, roll-up, and regeneration modes. The bed pairs behave identically, with cycles staggered by half of one adsorption - desorption - regeneration period. The cycle for each pair involves regeneration of one bed with dry air, while the other is cleaning the flue gas and subsequently rolling up the SO2. This bench-scale CCS is able to split a 6 standard liters per minute (SLPM) gas stream containing 2000 ppm SO2 into two streams of equal flowrate, one containing 3400 ppm SO2 and the other 70 ppm SO2. The influence of water is strong, with the rollup being optimal at 13% moisture in the flue gas. Adsorption starting with the bed at 75 degrees C is optimal, and air regeneration at 200 degrees C and 8 SLPM for 76 min is adequate. An economic analysis of an industrial-scaled CCS capable of treating a 1 000 000 scfm flue gas stream containing 2000 ppm SO2 (typical of a 400-MW coal-fired power plant) was conducted. The CCS installation permits smaller flue gas scrubbers to be installed and can potentially save a 400-MW power plant $2.6 million in annual operating costs.

The secondary structure of proteins in E.coli inclusion bodies was investigated via Raman spectroscopy. Inclusion bodies were purified from cells expressing different forms of RTEM beta-lactamase and grown at either 37 or 42-degrees-C. All of the solid phase inclusion body samples examined gave amide I band spectra that were perturbed from that of the native, purified protein in both solution and powder forms; secondary structure estimates indicated significant decreases in alpha-helix and increases in beta-sheet contents in the inclusion body samples. The structure estimates for inclusion bodies isolated from 37-degrees-C cultures were similar, regardless of aggregate localization in the E.coli cytoplasmic or periplasmic spaces or beta-lactamase precursor content. Inclusion bodies obtained from 42-degrees-C cells exhibited a further reduction of alpha-helix and augmentation of beta-sheet contents relative to those from 37-degrees-C cultures. These results are consistent with the paradigm for inclusion body formation via the self-association of intracellular folding intermediates having extensive secondary structure content. Further, the overall secondary structure content of inclusion bodies is not significantly affected by subcellular compartmentalization, but may be altered at increased temperatures.