Applied Catalysis B, Environmental (v.79, #4)

Contents (CO4).

Biomorphic SiC pellets as catalyst support for partial oxidation of methane to syngas by Qing Wang; Wei-Zhong Sun; Guo-Qiang Jin; Ying-Yong Wang; Xiang-Yun Guo (307-312).
Biomorphic silicon carbide (bioSiC) pellets prepared from carbonized millet were employed as nickel catalyst support for the partial oxidation of methane to syngas in a fixed-bed quartz reactor at 800 °C. To reduce the loss of nickel active component during the reaction, alumina was used to modify the bioSiC surface. The temperature programmed reduction reveals that the alumina modification can evidently increase the reduction temperature of nickel oxide and therefore enhance the interaction between nickel and support. Due to the enhanced interaction, the nickel component becomes stable and difficult to migrate on the support surface. As a result, the modified bioSiC catalyst shows higher catalytic activity and stability than the unmodified. Compared with the catalyst supported on powdered SiC, the pelletized catalyst shows higher activity, especially at high gas hourly space velocity.
Keywords: Partial oxidation of methane; Ni/bioSiC catalyst; Ni/bioSiC–Al2O3 catalyst;

The performance of platinum-tin catalysts, supported on Al2O3 and SiO2 and subjected to reduction prior to use, has been studied. The catalysts were characterized in reduced forms by X-ray diffraction (XRD) and XPS. The surface properties were determined by N2 BET specific surface area and CO chemisorption. The model compounds were 4,6-dimethyldibenzothiophene (4,6DMDBT) and carbazole. The PtSn catalysts supported on either Al2O3 or SiO2 were characterised by high activity, but the catalyst PtSn/SiO2 was found the most effective, even more effective than the commercial KF848 catalyst. Both PtSn catalysts studied were more effective in the reaction of 4,6DMDBT hydrogenation, the dominant product obtained with the use of PtSn/Al2O3 was methyl-cyclohexyltoluene (MCHT) and with PtSn/SiO2 the dominant product was dimethylbicyclohexyl (DMBCH). The amount of dimethylbiphenyl (DMBPh) obtained was small and practically independent of the contact time. In the HDN reaction of carbazole the most active was PtSn/SiO2. It was also more active in the consecutive reaction of isomerisation of the main product of the HDN reaction, bicyclohexyl (BCH) to methylcyclopentylcyclohexane (MCPCH). The large differences shown in the hydrotreating activity specially in the HDN reaction between PtSn catalysts supported on Al2O3 and SiO2 result from the physicochemical properties of both samples. The significantly higher CO chemisorption for PtSn/SiO2 indicates the presence of larger amount of metallic species and better hydrogenation properties so important for deep hydrotreating process.
Keywords: Hydrodesulphurisation; Hydrodenitrogenation; 4,6-Dimethyldibenzothiophene; Carbazole; Platinum; Tin; Alumina and silica supports; Commercial catalyst-KF848;

Effect of acid and base sites on the degradation of sulfur mustard over several typical oxides by Hairong Tang; Zhenxing Cheng; Haiyan Zhu; Guomin Zuo; Ming Zhang (323-333).
The reactions of the chemical warfare agent sulfur mustard (HD) degradation over CaO, MgO, SiO2, Al2O3, HZSM-5, A-Clays were studied. More than 10 kinds of products from the degradation of HD over these oxides were detected and identified by GC-FPD, GC–MS, NMR and UV–vis approaches. All the studied oxides can exhibit reactivity towards destroying HD molecules in air at room temperature. The acid and base sites over the oxides were not entirely poisoned by H2O and CO2 in air as evidenced by the acid–base property characterization results. The conserved acid and base sites over the oxides might be the reaction center for degradation of HD molecules. Both degradation activity and product distribution were strongly determined by the strength and density of the acid–base sites and the adsorbed water over the oxides.
Keywords: Mustard; Degradation; Oxide; Acid and base sites;

In this paper, the synthesis of AgBr/TiO2 catalyst and the photocatalytic activity in water under simulated sunlight irradiation were studied. The influence of AgBr content in catalyst and the incident light intensity on the degradation of methyl orange (MO) was investigated. It was found that the initial reaction rate constant was dependent on the relative levels of AgBr content and incident light intensity, ranging between 0.008 min−1 and 0.023 min−1. At higher levels of AgBr content (>9 wt%), MO degradation was exclusively dependent on the incident light intensity, which implied that the excessive AgBr in catalyst had negligible effect on catalyst activity. However, at lower AgBr contents, the reaction rate increased with the increase of incident light intensity, and eventually reached a plateau level, indicating that the degradation of MO was limited by AgBr content. The results from powder X-ray diffraction (XRD) analysis showed that more than 80% of AgBr remained intact after 14 h of irradiation, although metallic silver was also detected.
Keywords: Photocatalysis; AgBr/TiO2 catalyst; Simulated sunlight irradiation; Advanced oxidation technology (AOT); Methyl orange;

Pt monolayers deposited on carbon-supported Ru and Rh nanoparticles were investigated as electrocatalysts for ethanol oxidation. Electronic features of the Pt monolayers were studied by in situ XANES (X-ray absorption near-edge structure). The electrochemical activity was investigated by cyclic voltammetry and cronoamperometric experiments. Spectroscopic and electrochemical results were compared to those obtained on carbon-supported Pt–Ru and Pt–Rh alloys, and Pt E-TEK. XAS results indicate a modification of the Pt 5d band due to geometric and electronic interactions with the Ru ant Rh substrates, but the effect of withdrawing electrons from Pt is less pronounced in relation to that for the corresponding alloys. Electrochemical stripping of adsorbed CO, which is one of the intermediates, and the currents for the oxidation of ethanol show faster kinetics on the Pt monolayer deposited on Ru nanoparticles, and an activity that exceeds that of conventional catalysts with much larger amounts of platinum.
Keywords: Ethanol electro-oxidation; Platinum–ruthenium alloy; Platinum–rhodium alloy; Pt monolayer;

To retard the sintering, a series of transition metals were added to the low-temperature SCR catalysts based on Mn/TiO2, and activity of these catalysts was investigated. It was found that the transition metal had significant effects on the catalytic activity. With the addition of transition metals, more NO could be removed at lower temperature. The temperature of 90% NO conversion could decrease to 361 K by using Fe(0.1)–Mn(0.4)/TiO2. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction spectra (EDS) indicated that manganese oxides and titania could be better dispersed in the catalyst, and higher catalytic activity was obtained. From X-ray photoelectron spectrum (XPS) it could be known that solid solution was formed among the transition metal, manganese oxides and titania. With the formation of this solid solution, the Brunauer–Emmett–Teller (BET) area and pore volume increased. Furthermore, the in situ diffuse reflectance infrared transform spectroscopy (DRIFT) results showed that by using these catalysts, more NO could be oxidized to NO2 and nitrate, and then reacted with NH3. Therefore, the catalytic activity was greatly improved by the addition of transition metals.
Keywords: Sol–gel method; NO removal; Low-temperature SCR; Transition metal; Solid solution;

In this work, comprehensive investigation was done on the oxygen partial pressure-dependent behavior of the various catalysts using a flow-type plasma-driven catalyst (PDC) reactor. These data provide a useful guideline for the optimization of the cycled system using adsorption and the O2 plasma-driven catalysis of adsorbed volatile organic compounds (VOCs). The potentials of the tested catalysts for the cycled system were evaluated based on the enhancement factor and the adsorption capability. All the tested materials (TiO2, γ-Al2O3, zeolites) exhibited positive enhancement factor, while negative values with the dielectric-barrier discharge (DBD) plasma alone. TiO2 catalysts showed the highest enhancement factor of about 100 regardless of the type of metal catalysts and their supporting amount. Based on the experimental findings in this study and the literature information, a plausible mechanism of plasma-driven catalysis of VOCs was suggested.
Keywords: Nonthermal plasma; Oxygen plasma; VOCs; Total oxidation; Catalyst; Enhancement factor;

Photocatalytic oxidation of aliphatic and aromatic sulfides in the presence of silica adsorbed or zeolite-encapsulated 2,4,6-triphenyl(thia)pyrylium by Sergio M. Bonesi; Esther Carbonell; Hermenegildo Garcia; Maurizio Fagnoni; Angelo Albini (368-375).
Solid photocatalysts in which the 2,4,6-triphenylpyrylium (TP) or 2,4,6-triphenylthiapyrylium cation (TTP) are encapsulated within zeolite Y or deposited on mesoporous silica are used as photosensitizers for the oxidation of sulfides, both aromatic and aliphatic, in solvents of various polarity. Contrary to the same cations in solution, these solid sensitizers are not significantly degraded during operation. An effective oxygenation takes place leading to sulfoxides, disulfides, sulfinic and sulfenic esters as well as sulfonic acids. This large scope method shows a limited dependence on the substrate structure and on conditions and is suitable for the abatement of sulfur-containing pollutants.
Keywords: Photocatalyst; Sulfides; Oxidation; 2,4,6-Triphenylpyrilium; Zeolite;

Mechanism of enhanced photocatalysis with polyhydroxy fullerenes by Vijay Krishna; David Yanes; Witcha Imaram; Alex Angerhofer; Ben Koopman; Brij Moudgil (376-381).
Polyhydroxy fullerenes (PHF) have been applied for increasing the photocatalytic degradation rate of TiO2. Scavenging of photo-generated electrons and therefore higher generation of hydroxyl radicals was hypothesized as the mechanism for the observed enhancement. The present study confirms the increase in generation of hydroxyl radicals with electron paramagnetic resonance (EPR) spectroscopy. The concentration of hydroxyl radicals generated by a mixture of TiO2 and PHF was up to 60% greater than the concentration obtained without PHF. These results are consistent with the observed enhancement in dye degradation and microbial inactivation experiments. The current study also demonstrates that PHF can improve the photocatalytic activity of different TiO2.
Keywords: EPR; Hydroxyl radicals; Titanium dioxide; Escherichia coli; Procion red; Degussa P25; Anatase; Nanoparticles; Disinfection; Fullerols;

On an anodic alumina supported silver catalyst with a low Ag loading (1.68 wt.%), NO x (NO/He, NO/O2/He, NO2/He) adsorption measurements and NO x -temperature programmed decomposition (TPD)/temperature programmed surface-reaction (TPSR) measurements in different gas streams (He, C3H6/He, C3H6/O2/He) were conducted to investigate the formation, consumption and reactivity of surface adsorbed NO x species.During NO adsorption, no noticeable uptake of NO was detected. Introducing oxygen greatly improved the formation of ads-NO x species. A greater quantity of surface nitrate species was found after NO2 adsorption, accompanied with gaseous NO release. The result of TPSR demonstrates the surface nitrate species can be effectively and preferentially reduced by propene. When introducing oxygen into the propene gas stream of TPSR test, the significantly increased amount of reacted nitrate undoubtedly shows the importance of oxygen in activating propene. The pathway for the selective reduction of NO x in the presence of excess oxygen is proposed to pass through the selective reduction of the adsorbed nitrate species with the activated propene.The enhanced NO x conversion when replacing NO with NO2 was attributed to the stronger NO x adsorption capacity and oxidation ability of NO2, than those for NO. With increasing oxygen concentration, the difference between NO and NO2 would gradually decrease, and finally disappear in a high excess of oxygen.
Keywords: Ag; Anodic alumina; TPD/TPSR; Selective catalytic reduction; De-NO;

Gold loaded on TiO2 (Au/TiO2) catalysts were prepared using Au(I)–thiosulfate complex (Au(S2O3)2 3−) as the gold precursor for the first time. The samples were characterized by UV–vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), and X-ray photoelectron spectroscopy (XPS) methods. Using Au(S2O3)2 3− as gold precursor, ultra-fine gold nanoparticles with a highly disperse state can be successfully formed on the surface of TiO2. The diameter of Au nanoparticles increases from 1.8 to 3.0 nm with increasing the nominal Au loading from 1% to 8%. The photocatalytic activity of Au/TiO2 catalysts was evaluated from the analysis of the photodegradation of methyl orange (MO). With the similar Au loading, the catalysts prepared with Au(S2O3)2 3− precursor exhibit higher photocatalytic activity for methyl orange degradation when compared with the Au/TiO2 catalysts prepared with the methods of deposition–precipitation (DP) and impregnation (IMP). The preparation method has decisive influences on the morphology, size and number of Au nanoparticles loaded on the surface of TiO2 and further affects the photocatalytic activity of the obtained catalysts.
Keywords: Au/TiO2; Photocatalytic activity; Degradation; Au(S2O3)2 3−; Au loading;

Monodispersed gold nanoparticles supported on γ-Al2O3 for enhancement of low-temperature catalytic oxidation of CO by Li Wen; Jin-Kun Fu; Ping-Ying Gu; Bing-Xing Yao; Zhong-Hua Lin; Jian-Zhang Zhou (402-409).
Monodispersed nano-Au/γ-Al2O3 catalysts for low-temperature oxidation of CO have been prepared via a modified colloidal deposition route, which involves the deposition of dodecanethiolate self-assembled monolayer (SAM)-protected gold nanoparticles (C12 nano-Au) in hexane on γ-Al2O3 at room temperature. The diameter of the gold nanoparticles deposited on the support is 2.5 ± 0.8 nm after thermal treatment, and their valence states comprise both the metallic and oxidized states. It is found that the thermal treatment temperature affects significantly the catalytic activity of the catalysts in the processing steps. The catalyst treated at 190 °C exhibits considerably higher activity as compared to catalysts treated at 165 and 250 °C. A 2.0-wt.% nano-Au/γ-Al2O3 catalyst treated at 190 °C for 15 h maintains the catalytic activity at nearly 100% CO oxidation for at least 800 h at 15 °C, at least 600 h at 0 °C, and even longer than 450 h at −5 °C. Evidently, the catalysts obtained using this preparation route show high catalytic activity, particularly at low temperatures, and a good long-term stability.
Keywords: Gold catalyst; Alumina support; Gold nanoparticle; CO oxidation; Monodispersity;