BiVO(4) films were prepared by a simple electrodeposition and annealing procedure and studied as oxygen evolving photoanodes for application in a water splitting photoelectrochemical cell. The resulting BiVO(4) electrodes maintained considerable photocurrent for photo-oxidation of sulfite, but generated significantly reduced photocurrent for photo-oxidation of water to oxygen, also decaying over time, suggesting that the photoelectrochemical performance of BiVO(4) for water oxidation is mainly limited by its poor catalytic ablity to oxidize water. In order to improve the water oxidation kinetics of the BiVO(4) electrode, a layer of FeOOH was placed on the BiVO(4) surface as an oxygen evolution catalyst using a new photodeposition route. The resulting BiVO(4)/FeOOH photoanode exhibitied significantly improved photocurrent and stability for photo-oxidation of water, which is one of the best among all oxide-based phoatoanode systems reported to date. In particular, the BiVO(4)/FeOOH photoanode showed an outstanding performance in the low bias region (i.e., E < 0.8 V vs RHE), which is critical in determining the overall operating current density when assembling a complete p-n photoelectrochemical diode cell. The photocurrent-to-O(2) conversion efficiency of the BiVO(4)/FeOOH photoanode is ca. 96%, confirming that the photogenerated holes in the BiVO(4)/FeOOH photoanode are indeed excusively used for O(2) evolution.

Efficient and stable photo-oxidation of water by a bismuth vanadate photoanode coupled with an iron oxyhydroxide oxygen evolution catalyst.

The most widely used catalysts and processes for H2S-selective catalytic oxidation are overviewed in this review. Two kinds of catalysts have been investigated intensively: carbon-based catalysts (active carbon catalyst, carbon nanotube catalyst, and carbon nanofiber catalyst), metal oxide-based catalysts (metal oxide catalyst, oxide-supported catalyst, and clay-supported catalyst). Among them, carbon-based catalysts are utilized mainly in discontinuous processes at relatively low temperatures, whereas metal oxide catalysts are the most widely used in practice. However, the reaction temperature is relatively high. Fortunately, a MgAlVO catalyst derived from LDH materials and intercalated clay-supported catalysts exhibit excellent catalytic activities at relatively lower temperatures. According to various studies, the catalytic behaviors mainly obey the Mars–van Krevelen mechanism; however, the catalyst deactivation mechanism differs, depending on the catalyst. In practice, the mobil direct oxidation proce...

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H2S-Selective Catalytic Oxidation: Catalysts and Processes

Elements and their compounds in the environment: occurrence, analysis and biological relevance.

Natural gas, refinery gas, and coal gas contain acid gases such as hydrogen sulfide (H 2 S) and carbon dioxide that must be removed from the gas stream due to the toxicity of H 2 S and to prevent corrosion to piping and production facil- ity caused by the acid gases. In this article, current technolo- gies for the acid gas removal are selected and reviewed. The review includes absorption, adsorption, conversion of H 2 S into elemental sulfur, and membrane reactor for H 2 S decom- position and desulfurization. Recently, hollow fiber mem- brane contactor has been in the limelight of research in H 2 S absorption from gaseous mixture due to its potential to over- come problems such as foaming and loading. Recent trends on Claus tail gas cleanup technologies are highlighted due to the recent progress in membrane technology. The article also suggests current research on the acid gas removal technol- ogy using catalytic membrane reactor. The interest on find- ing suitable active component and support and studying the membrane structure for enhanced removal of acid gases is likely to be rekindled in the near future.

Present technologies for hydrogen sulfide removal from gaseous mixtures

Mo-doped BiVO4 electrodes were prepared by an electrochemical route for use as photoanodes in a photoelectrochemical cell. The purpose of Mo-doping was to improve the electron transport properties, which in turn can increase the electron–hole separation yield. The poor electron–hole separation yield was known to be one of the main limiting factors for BiVO4-based photoanodes. The electrochemical route provided an effective way of doping BiVO4, and the optimally doped sample, BiV0.97Mo0.03O4, increased the electron–hole separation yield from 0.23 to 0.57 at 0.6 V vs. RHE, which is a record high separation yield achieved for BiVO4-based photoanodes. As a result, BiV0.97Mo0.03O4 generated impressive photocurrents, for example, 2 mA cm−2 at a potential as low as 0.4 V vs. RHE for sulfite oxidation, which has fast oxidation kinetics and, therefore, the loss of holes by surface recombination is negligible. For photooxidation of water, BiV0.97Mo0.03O4 was paired with FeOOH as an oxygen evolution catalyst (OEC) to improve the poor catalytic ability of BiV0.97Mo0.03O4 for water oxidation. The resulting BiV0.97Mo0.03O4/FeOOH photoanodes generated a significantly improved photocurrent for water oxidation compared to previous reported results, but the photocurrent of BiV0.97Mo0.03O4/FeOOH for water oxidation could not reach the photocurrent of BiV0.97Mo0.03O4 for sulfite oxidation. In order to examine the cause, the effects of Mo-doping on the interaction between BiVO4 and FeOOH and the effects of FeOOH on the electron–hole separation yield of BiV0.97Mo0.03O4 were investigated in detail, which provided new insights into semiconductor–OEC interactions.

Marked enhancement in electron–hole separation achieved in the low bias region using electrochemically prepared Mo-doped BiVO4 photoanodes

The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was studied over V-Sb-O/TiO 2 catalyst. They showed very high conversion of H 2 S without any harmful emission of SO 2 . The investigation was focused to understand the roles of several oxides. Therefore, V 2 O 5 /SiO 2 , V 2 O 5 /TiO 2 , the mechanical mixture catalyst (V 2 O 5 +Sb 2 O 4 ) and V-Sb-O/TiO 2 are studied separately. TiO 2 support increased the activity and stability of V 2 O 5 . Sb 2 O 4 increased the reoxidation of reduced V 2 O 5 by supplying spillover oxygen through the boundaries of the metal oxides. VSbO 4 was one of the main active phase in V-Sb-O/TiO 2 mixed oxides.

Vanadium-antimony mixed oxide catalysts for the selective oxidation of H2S containing excess water and ammonia

Highly ordered VSBA-15 mesoporous catalysts have been synthesized under pH-adjusting direct hydrothermal (pH-aDH) method using vanadyl sulphate hydrate and Pluronic P123 as the sources of vanadium and template, respectively. The mesoporous catalysts characterized by sophisticated instrumental techniques, viz. ICP-AES, XRD, N 2 adsorption, ESR, UV–vis DRS, 51 V MAS NMR, 29 Si MAS NMR and TEM show their two-dimensional mesostructures with tetrahedral vanadium species on the silica surface. The well ordered VSBA-15 catalysts have been used in the oxidation of cyclododecane (CDD) with hydrogen peroxide (H 2 O 2 , 30%) to find their catalytic activities. The regenerated VSBA-15 catalysts have been examined to find their catalytic stabilities. VSBA-15(5) catalyst has been washed with ammonium acetate solution to investigate the leaching of vanadium species in the framework of silica network of SBA-15, and the catalytic activity of washed VSBA-15(5) has also been examined in the catalytic reactions. Moreover, the hydrothermally stable VSBA-15(5) catalyst has also been examined in the catalytic reaction to find the effect of its catalytic activity. Additionally, the influences of various reaction parameters such as temperature, time, ratios of reactant and solvents on the oxidation of CDD have been investigated. Based on the catalytic results, VSBA-15(5) catalyst is found to be a highly active, recyclable and promising heterogeneous catalyst for selective synthesis of cyclododecanone (CDD O).

Highly selective synthesis of cyclododecanone over mesostructured VSBA-15 catalysts

In the present study, synthesis of (2-oxo-l,3-dioxolan-4-yl)methyl vinyl ether(OVE) from carbon dioxide and glycidyl vinyl ether(GVE) was investigated using quaternary ammonium salts as catalyst. Among the salts tested, the one having larger alkyl group and more nucleophilic counter anion exhibited a better catalytic activity. Polymers bearing pendant 5-membered cyclic carbonate groups were prepared by radical copolymerization of OVE with acrylonitrile. The monomer reactivity ratio could be estimated as r1(OVE)=0.36 and r2(AN)=1.21 by Finemann-Ross method. The miscibility of blends containing poly(OVE-co-AN) and poly(styrene-co-acrylonitrile)(SAN) has been studied by the optical clarity and DSC. All of the OVE-AN/SAN blends studied were miscible.

Catalytic conversion of carbon dioxide to polymer blends via cyclic carbonates

Well hexagonally ordered CrSBA-15 catalysts synthesized by different hydrothermal methods were used, for the first time, for the selective synthesis of benzophenone (BP O) by liquid-phase oxidation of diphenylmethane (DPM) under various reaction conditions. To investigate the leaching of chromium species on the surface of silica networks, the results of original and reusable Cr-containing mesoporous silica catalysts were correlated and compared, and the catalytic activity of washed CrSBA-15(8) was also demonstrated. Based on the all catalytic results for this reaction, CrSBA-15(8) was found to be a highly active and an environmentally friendly solid catalyst and has superior catalytic activity than other Cr-containing mesoporous catalysts.

Selective synthesis of benzophenone over two-dimensional mesostructured CrSBA-15

The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over vanadium-bismuth mixed oxide catalysts. The investigation was focused on understanding the complex reaction steps and the roles of each metal oxide. Therefore, supported V2O5/TiO2, V-Bi-O/TiO2 catalysts and a mechanical mixture of V2O5 + Bi2O3 were tested in the reaction. Ammonia reacted either with H2S or SO2, produced from the oxidation of H2S. Water vapor promoted the reaction of ammonia and SO2. Strong synergistic phenomena in catalytic activity were observed for the mechanically mixed catalyst of V2O5 and Bi2O3. V-Bi-O/TiO2 catalyst showed very high H2S conversion without any considerable emission of SO2. Temperature-programmed studies (TPR and TPO), XRD and Raman analyses revealed that the high catalytic performance of V-BiO/TiO2 catalyst originated from the high redox capacity of the bismuth vanadate phase.

Dae-Kwang Park

Papers

Vanadium-antimony mixed oxide catalysts for the selective oxidation of H2S containing excess water and ammonia

Highly selective synthesis of cyclododecanone over mesostructured VSBA-15 catalysts

Catalytic conversion of carbon dioxide to polymer blends via cyclic carbonates

Selective synthesis of benzophenone over two-dimensional mesostructured CrSBA-15

Selective oxidation of hydrogen sulfide to ammonium thiosulfate and sulfur over vanadium-bismuth oxide catalysts