The catalytic active centers and the additive effects on catalytic active centers have been studied by spectrophotometric (UV-VIS) and spectroscopic (Raman, NMR) methods at high temperatures for the molten salt-gas system M2S2O7/MHSO4/M2SO4/V2O5 - SO2/O2/SO3/CO2/H2O/N2 (or parts of this system) which is considered a realistic model of the working industrial catalysts used for sulfuric acid production and removal of SO2 from flue gas. For the first time, high temperature vibrational spectra have been obtained for the very dark, viscous and hygroscopic V2O5-M2S2O7M2SO4 (M= alkali metal) melts and the spectra obtained are conclusively interpreted. A series of vanadium compounds in the oxidation state III, IV, V and of mixed valence V(IV)-V(V) have been isolated from catalyst model systems and characterized by thermal, spectroscopic and X-ray methods. These compounds are identified as catalyst deactivation products. Various physicochemical properties for the above complex molten salt-gas system (specific conductivities, heat capacities, vapor pressures etc.) have been established. Equilibrium vapor pressures over KHSO4-K2S2O7 and V2O5-KHSO4-K2S2O7 systems at 20-500 C were defined using the Boiling point method, the Quartz-Bourdon method and a newly developed vapor pressure measurement technique which can be used for measurements in the region from 10 torr to 10 bar. Two unique versatile apparatuses enabling combined catalytic activity measurements and real-time spectroscopic (ESR, UV-VIS) studies of commercial catalysts and catalyst model systems in SO2 containing gases (or in any gas mixture) up to 1200 K have been constructed. The results obtained on SO2 oxidation catalysts show good accordance between temperature of catalyst deactivation and the simultaneous precipitation of V(IV) or V(III) compound as detected by ESR. The complex and redox chemistry of vanadium in the catalyst solvent melt have also been investigated by means of spectroscopic and electrochemical methods at high temperatures. Furthermore, phase diagrams of the catalyst model systems M2S2O7-V2O5 (M = Na, K, Cs) and KHSO4-K2S2O7 have been constructed. The results are considered useful for understanding the mechanism of SO2 oxidation by alkali promoted V2O5 catalysts at the molecular level, for exploring the routes of catalyst deactivation experienced at temperatures below 400 C and for the design of modified catalysts with high activity also below 400 C.
The project is directed at establishing the physical and chemical factors leading to : i) a modified catalyst for the production of sulfuric acid which will be active at lower temperatures (<400 C) than the catalyst used today and ii) an improved molten salt catalyst for SO2 removal from flue-gas.
Research which defines the fundamental physical and chemical factors leading to enhanced low temperature activity wil provide the scientific bases for developing a modified sulfuric acid catalyst and an improved catalyst for SO2 removal from flue gas without the need of large scale iterative trials.
The investigations will be concerned with industrial catalysts and the liquid-gas system M2S2O7/MHSO4/V2O5 - SO2/O2/SO3H2O/N2, where M=Na, K, Cs, corresponding to the various catalyst promotors in the temperature range 200 C - 600 C.
The investigation of the catalytic oxidation of SO2 will be performed by two highly specialized partners with the use a multiinstrumental research strategy involving kinetic, spectroscopic, electrochemical, magnetic, thermal and X-ray methods on catalysts and model melts at high temperatures and to solids obtained from the catalytic systems. Selected catalysts and model melts will be the subject of thorough labscale activity tests by use of versatile molten salt catalyst test equipments.
Funding SchemeCSC - Cost-sharing contracts