Electrochemical Study on the Cationic Promotion of the Catalytic  SO 2 Oxidation in Pyrosulfate Melts

Abstract

The electrochemical behavior of the molten V,O,-M,S,O, (M = K, Cs, or Na) system was studied using a gold working electrode at 440°C in argon and air atmosphere. The aim of the present investigation was to find a possible correlation between the promoting effect of Cs + and Na + ions on the catalytic oxidation of SO, in the V,O,-M,S,O, system and the effect of these alkali cations on the electrochemical behavior of V,O, in the alkali pyrosulfate melts. It has been shown that Na + ions had a promoting effect on the V(V) 4 V(IV) electrochemical reaction. Sodium ions accelerate both the V(V) reduction and the V(IV) oxidation, the effect being more pronounced in the case of the V(IV) oxidation. Sodium ions also had a significant (almost 0.2 V) depolarization effect on the V(IV) -V(V) oxidation. The peak current of the V(IV) -V(V) oxidation waves vs. Na,S,0 7 concentration plots had maximums at ca. 8.5 mol % of NaS207 in air atmosphere for all the studied potential scan rates. In the Cs2S20,-K,S20, (1:1) melt the V(IV) -V(V) oxidation was affected by Cs + ions with a depolarization effect of 0.2 V and an even more significant acceleration than the in molten V,O,-Na,S2,O,-K,S,O, system. The V(IV) -V(V) oxidation peak currents were approximately 1.5 times higher than in the V2,O,-K2S20, system at all studied potential scan rates. No correlation has been found between the described effects and the electric conductivity of the systems. The rate-determining stage in the catalytic SO, oxidation most likely is the oxidation of V(IV) to V(V) and the Na + and Cs + promoting effect is based on the acceleration of this stage. It has also been proposed that voltammetric measurements can be used for fast optimization of the composition of the vanadium catalyst (which is approximately V,O,-M2S207) for sulfuric acid production.

Structure of Vanadium Oxosulfato Complexes in V2O5−M2S2O7−M2SO4 (M = K, Cs) Melts. A High Temperature Spectroscopic Study

“…So far, various methods including potentiometry, cryoscopy, spectrophotometry, conductometry, calorimetry, NMR, cyclic voltammetry, and Raman spectroscopy have been used to study the V V complexes in V 2 O 5 −M 2 S 2 O 7 −M 2 SO 4 (M = K, Cs) melts. − The phase diagrams of the V 2 O 5 −M 2 S 2 O 7 (M = 80% K + 20% Na), V 2 O 5 −K 2 S 2 O 7 , V 2 O 5 −Cs 2 S 2 O 7 , and V 2 O 5 −Rb 2 S 2 O 7 systems have been constructed. The only V V compounds isolated from the V 2 O 5 −M 2 S 2 O 7 molten systems and characterized by single-crystal X-ray study are the Cs 4 (VO) 2 O(SO 4 ) 4 , Rb 4 (VO) 2 O(SO 4 ) 4 , , and K 4 (VO) 2 O(SO 4 ) 4 . , …”

Electrochemical Promotion of Sulfur Dioxide Catalytic Oxidation

“…The third gold wire electrode inserted in the counter electrode compartment outside the gas inlet tube was used as a quasi-reference electrode. It has been shown in our own publications [1][2][3] that in the studied media the potential of the gold electrode is defined by the redox couple V(V) } V(IV). This reaction is reversible and the reference electrode has a stable potential.…”

“…The present work is a continuation of our investigation of the electrochemistry of the molten V 2 O 5 -M 2 S 2 O 7 system (M is an alkali metal). [1][2][3] This melt has been found to be a realistic model of the V 2 O 5 -M 2 S 2 O 7 catalyst for sulfur dioxide oxidation with air which is used in sulfuric acid production and SO 2 removal from flue gases. It has been shown [1][2][3] that electrochemical measurements can provide important information about the vanadium complexes formed in the K 2 S 2 O 7 -V 2 O 5 and K 2 S 2 O 7 -KHSO 4 -V 2 O 5 molten systems and thus provide some insight concerning the reaction mechanism during catalysis.…”

“…[1][2][3] This melt has been found to be a realistic model of the V 2 O 5 -M 2 S 2 O 7 catalyst for sulfur dioxide oxidation with air which is used in sulfuric acid production and SO 2 removal from flue gases. It has been shown [1][2][3] that electrochemical measurements can provide important information about the vanadium complexes formed in the K 2 S 2 O 7 -V 2 O 5 and K 2 S 2 O 7 -KHSO 4 -V 2 O 5 molten systems and thus provide some insight concerning the reaction mechanism during catalysis. It has also been concluded that the voltammetric technique can be used to examine the alkali ion promotion effect on the V(V) } V(IV) reaction in this system.…”

Monitoring the Dissolution and Hydrolysis of Pyrosulfate by Electrochemistry at a Liquid‐Liquid Microinterface Array

“…Pyrosulfate (disulfate, S 2 O 7 2À ), which is easily hydrolysed, [13] has an important role in various industrial processes, such as decomposition of ore materials and alloys, and the production of sulfuric acid. [14,15] Recently, it has been used as a catalyst for the conversion of hemicellulose from barley straw to reducing sugars such as xylose and galactose, which are potential substrates for the production of fuels, including renewable hydrogen. [16] As an oxyanion, it has been used to stabilise tetravalent palladium [17] and as a component of a catalyst, diarylammonium pyrosulfate, [18] for ester hydrolysis.…”