Conductivity and Phase-Diagram of the SO2 Oxidation Catalyst Model System: M2S2O7-V2O5 (M=80% K + 20% Na)

Vanadia?silica and vanadia?cesium?silica catalysts for oxidation of SO2

“…The increase of loading results in formation of polymeric two-dimensional species in distorted tetrahedral and square-pyramidal coordination, and bulk V 2 O 5 crystals are formed when vanadia loading exceeds the monolayer coverage of the support. The addition of alkaline metal sulfates to vanadia catalysts leads, at higher temperatures, to molten salt mixtures, which exhibit low melting points [11,13,42,43].…”

Fused Catalysts

“…The point at which the activation energy for SO 2 oxidation changes over to a lower (transportcontrolled) value marks thus the point at which crystallisation of the supersaturated solution begins under catalytic conditions. This hypothesis could be verified in pioneering studies by Fehrmann and co-workers using electric conductivity measurements and preparative isolation techniques [17,16]. They isolated indeed crystals of a variety of V 4+ and V 3+ ternary alkali sulphates.…”

“…This hypothesis was verified in pioneering studies conducted by Fehrmann and coworkers using electric conductivity measurements and preparative isolation techniques [35,36]. The reaction mechanism, and the fact that the operation point of the catalyst is at the absolute minimum in the V 5+ -O 2 section of the phase diagram, point to the existence of a supersaturated solution of partly reduced vanadium oxides in the melt.…”

“…The real pseudo-binary phase diagram [35] of V 2 O 5 / S 2 O 7 M 2 with M = K or Na is rather complex in the interesting range around the eutectic, which is shown in Fig. 5.…”

“…[13,14,15]. The technical catalyst is a supported liquid phase system of vanadium pentoxide in potassium pyrosulfate [16,17]. Other alkali ions influence the activity [18] at the low-temperature end of the operation range with Cs exhibiting a particular beneficial effect [13].…”