Applied Catalysis B, Environmental (v.79, #2)

Contents (CO4).

Co/K x Ti2O5 catalysts prepared by ion exchange method for NO oxidation to NO2 by Qiang Wang; So Ye Park; Jin Seong Choi; Jong Shik Chung (101-107).
Co/K x Ti2O5 catalysts prepared by ion exchange method were tested for NO oxidation to NO2. Their catalytic activities are similar to Pt-based catalysts and much higher than Co impregnated on TiO2 with or without doped K. The conversion pattern shows a typical kinetic control at low temperatures and thermodynamic control at higher temperatures, exhibiting a peak temperature at which the conversion becomes a maximum. Conversion decreases sharply as oxygen concentration decreases below 1.0%. NO concentration shows a positive effect on the conversion. The presence of Co3O4 and K ion remaining in K x Ti2O5 after the ion exchange is responsible for the observed catalytic activity. Thus, Co/K x Ti2O5 having a complete ion exchange with little K is not active for the reaction. Unlike Pt-based catalyst, the presence of NO2 does not inhibit catalytic activity. Co/K x Ti2O5 was resistant to the presence of SO2 less than 10 ppm. High-NO oxidation activity and high resistance to SO2 and NO2 make Co/K x Ti2O5 a promising catalyst for NO oxidation.
Keywords: NO oxidation; Co/K x Ti2O5; Co/TiO2; SO2 poisoning;

Keywords: Heterogeneous catalysis; Langmuir Hinshelwood kinetics; Theory; Zero order kinetics;

The effect of H2O on the reduction of SO2 and NO by CO on La2O2S by Ngai T. Lau; Ming Fang; Chak K. Chan (110-116).
The effect of H2O on the catalytic reduction of SO2 and NO on La2O2S was studied using temperature-programmed reaction coupled with fast mass spectrometry, powder X-ray diffraction and X-ray photoelectron spectroscopy. It is found that La2O2S can be completely and irreversibly deactivated in the presence of H2O at 700 °C when NO/SO2 is sufficiently high (∼1.0). This is caused by the formation of a layer of inactive and stable La2O2SO4 on the oxysulfide. When NO is absent or NO/SO2 is low (∼0.4), H2O inhibits the reduction and shifts the selectivity from sulfur to H2S. While the causes of the deactivation can be attributed to the Reverse Claus Reaction between H2O and sulfur in the oxysulfide, the competitive hydrolysis of the COS intermediate and the competitive adsorption of H2O, the shift in selectivity to H2S is attributable to the former two factors.
Keywords: Lanthanum oxysulfide; Deactivation; Selectivity; Hydrogen sulfide; Hydrolysis;

Nano-sized TiO2 photocatalysts were prepared by hydrolysis of TiCl4 followed by calcination at different temperatures. X-ray diffraction (XRD) measurements revealed that all TiO2 powders crystallized in rutile even before calcination. The photocatalytic activity of the raw TiO2 powder clearly decreased with increasing calcination temperature. Pt-modification of the surface of TiO2 increased photocatalytic activity under visible-light irradiation, depending on the calcination temperature. Maximal photocatalytic activity was obtained at calcination temperatures of 300–450 °C, which was correlated with the light absorption properties of the Pt complex on TiO2 nano-particles. It was found that TiO2 surface structure plays an important role in the formation of Ti―O―Pt bonds, resulting in a large visible-light absorbance and high photocatalytic activity under visible-light irradiation.
Keywords: TiO2; Photocatalyst; Visible light; Platinum;

Palladium-manganese catalysts supported on monolith systems for methane combustion by J. Requies; M.C. Alvarez-Galvan; V.L. Barrio; P.L. Arias; J.F. Cambra; M.B. Güemez; A. Manrique Carrera; V.A. de la Peña O'Shea; J.L.G. Fierro (122-131).
Alumina-supported bimetallic and monometallic Mn and Pd monolithic catalysts were prepared and tested in methane combustion. Two different reactor configurations were adopted for catalyst testing, i.e. a fixed-bed laboratory-scale reactor and a pilot-plant reactor which allowed work at different temperatures and pressures. The results of catalyst performance showed that all bimetallic catalysts are considerably more stable for methane combustion than the monometallic palladium catalyst. With the aim to explain the relationship between activity-stability and structure and surface properties, the catalysts were characterized by TPO, XRD, XPS and ICP-AES. The high stability displayed by the bimetallic systems is attributed to the influence of manganese in retarding the decomposition of PdO into metallic palladium. Thus, it appears that manganese oxides inhibit PdO decomposition, as a consequence of the increase in oxygen mobility in the manganese oxide spinel phase.
Keywords: Catalytic combustion; Methane; Palladium; Manganese; Monolith; Alumina;

Supported Pd catalysts on various support materials, ZnO, Ga2O3, SiO2, CeO2, In2O3, and Al2O3, exhibit poor activity and selectivity for the selective oxidation of CO in H2-rich gas with O2. The most active catalyst is Pd/ZnO among the six samples examined. The Pd species exist in the form of PdZn alloy in this catalyst and the alloy is more effective for the reaction compared with metallic Pd species of the other catalysts. The activity of Pd/ZnO catalyst can be significantly improved by the addition of alkali compounds, in particular Cs and Rb. These additives were shown to enhance the CO oxidation but suppress the undesired H2 oxidation. With the optimized Cs-modified Pd/ZnO catalyst (Cs/Pd = 3), the CO concentration of a mixture of CO/O2/H2/CO2 (0.5/2.0/23/7.0) can be reduced to a 40 ppm level at 433 K, while controlling the H2 conversion level to <10%. Temperature programmed desorption measurements indicate that the addition of Cs affects the adsorption/desorption behavior of CO and H2 on PdZn alloy particles in the Pd/ZnO catalyst but not the size of PdZn alloy crystallites. The Cs promoter is effective to weaken the strength of CO adsorption on the catalyst and increase the amount of H2 weakly interacting with them in the presence of both CO and H2, resulting in the enhanced selective CO oxidation activity of the Cs-modified Pd/ZnO catalyst.
Keywords: Selective oxidation; CO removal; Supported Pd catalyst; PdZn alloy; Alkali promoter;

The states of gold species in CeO2 supported gold catalyst for formaldehyde oxidation by Yuenian Shen; Xuzhuang Yang; Yizheng Wang; Yanbing Zhang; Huaiyong Zhu; Ling Gao; Meilin Jia (142-148).
To develop HCHO oxidation catalysts which work at moderate temperatures, a series of Au/CeO2 catalysts with a gold content below 0.85 wt.% were prepared by co-precipitation and subsequent calcinations at 300 °C. Oxidation of formaldehyde on these catalysts at temperatures close to 100 °C was conducted, and the structures of catalysts were characterized by X-ray diffraction (XRD) and transmission electronic microscopy (TEM) techniques. Gold exists in highly dispersed crystallite clusters in these catalysts, and we did not observe any gold crystals larger than 2–3 nm. In contrast, the CeO2 support is well crystallized, the fringes from (1 1 1) lattice plane of the support CeO2 are very clear in the TEM image. Gold crystals with a mean size of about 10 nm formed in a sample containing 0.78 wt.% of gold (0.78Au) when it was calcinated at 400 °C for 2 h. However, the formation of larger gold crystals causes a decrease in the catalytic activity. It appears that the highly dispersed gold catalyst provides more active sites for the HCHO oxidation. When the sample 0.78Au was calcined at 700 °C for 2 h, large gold particles (≥50 nm) appeared and the activity for HCHO oxidation decreased further but was still better than that of ceria. XRD and XPS results show an interesting fact that some of gold was incorporated into lattice of ceria.
Keywords: Gold catalyst; Formaldehyde oxidation; Indoor air pollution; Ceria support; TEM analysis;

The catalytic combustions of benzene, toluene and o-xylene (BTX) were investigated over the copper based spent catalyst and the pretreated copper based spent catalysts as well. Air, hydrogen and five different acid aqueous solution (HNO3, CH3COOH, H2SO4, HCl, and H3PO4) pretreatments were employed to recycle the spent catalyst from chemical industry. The properties of the pretreated spent catalysts were characterized by the Brunauer Emmett Teller (BET), elemental analyzer (EA), inductively coupled plasma (ICP), temperature programmed reduction (TPR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. The results showed that while the air pretreatment had an insignificant effect on the catalytic activity of the spent catalyst, the hydrogen pretreatment significantly enhanced that of the spent catalyst. The temperature of hydrogen pretreatment also made a significant difference in its catalytic activity. Furthermore, the increasing pretreatment temperature increased the catalytic activity of the spent catalyst, which was associated with the lower copper oxidation state (or reduced state). In acid pretreatment, the order of catalytic performance of the pretreated spent catalyst according to each acid aqueous solution was found to be HNO3  > CH3COOH > none > HCl > H3PO4  > H2SO4. Nitric acid or acetic acid pretreatment slightly improved the catalytic activity of the spent catalyst by regenerating the active sites on the pretreated samples. The XRD, XPS and TPR results clearly supported that all copper species such as CuO, Cu2O and Cu0 were active, among which Cu0 was the most active for the removal of toluene. Hydrogen pretreatment was superior to air or acid pretreatments for regenerating the spent catalyst because it favored the generation of metallic coppers. Based on the results of a long-term test and the catalytic activity of BTX, we suggested that the copper based spent catalyst pretreated with hydrogen could be recycled for the removal of volatile organic compounds (VOCs).
Keywords: Catalytic combustion; Spent catalyst; Pretreatment; Recycle; VOCs;

Pd and Pd–Ag alloy membranes on porous alumina tubes were prepared by means of simultaneous and sequential electroless plating technique. The characterizations of Pd–Ag composite membranes were performed using scanning electron microscopy (SEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic reaction of H2 and O2 to directly form hydrogen peroxide was carried out in the membrane reactor at 293 K. The thickness of Pd–Ag alloy membranes obtained by simultaneous electroless plating was thinner than that by sequential electroless plating. And high uniformity of grains was found on the surface of the Pd–Ag membrane prepared by simultaneous electroless plating. The concentration of H2O2 increased with the increase in transmembrane pressure differences of hydrogen and a high concentration of H2O2 was obtained on the membrane which consists of a Pd layer on the surface of the membrane and a Pd–Ag alloy layer inside the membrane.
Keywords: Hydrogen peroxide; Pd–Ag composite membrane; Direct synthesis; Membrane reactor;

A combination of ferric chloride and sodium nitrite is a competent catalyst for catalytic bleaching of a broad range of dye pollutants under moderate condition (T  = 150 °C; oxygen pressure = 0.5 MPa; pH 2.5). To evaluate the catalytic degradation system, we implemented wet oxidation of Acid Blue 129 (AB129) at the temperatures between 110 and 150 °C using FeCl3/NaNO2 as the catalyst. The degradation process was monitored by UV–vis spectroscopy, HPLC, IC, GC–MS and TOC analysis. At 150 °C and 0.5 MPa oxygen, 50.9% TOC and 100% color were removed after 2 h treatment, while no obvious TOC and only 20.4% color removal were achieved without the catalyst at the same experimental conditions. The main degradation products detected were CO2 and some small organic acids. The reaction kinetics of the process was also studied in the temperature range of 120–150 °C. AB129 degradation can be described by pseudo-first-order kinetics over the temperature range. Furthermore, this catalytic system is also highly efficient for tackling a variety of substrates including azo and anthraquinone dye pollutants.
Keywords: Catalytic wet oxidation; Ferric chloride; Sodium nitrite; Dye pollutants; Acid Blue 129;

Photocatalytic oxidation (PCO) tests were carried out for toluene adsorbed on the activated carbon fibers (ACFs)-supported TiO2 photocatalyst in an environmental condition controlled chamber. TiO2/ACF catalyst was made and characterized by N2 adsorption isotherm for pore structure and scanning electron microscopy (SEM) for morphology, respectively. Through exploring the remnant of toluene and the accumulation of intermediates on the TiO2/ACF catalyst including species, amount and their change processes under different relative humidity (RH), this study aimed to explore the influence of RH on the PCO of toluene and the roles of water vapor in the PCO process: PCO reaction paths and the accumulation of intermediates on the TiO2/ACF catalyst. Results showed that (1) with the increase of RH in the chamber (15%, 30%, 45% and 60%) the PCO conversion rate of toluene was positive correlated and no catalyst deactivation was observed under all RH levels; (2) during the gas–solid PCO process of toluene, byproducts of aromatic ring oxidation including 2-methyl, p-benzoquinone and o(m, p)-cresol were observed on the TiO2/ACF catalyst which had not been reported, together with the intermediates of side chain oxidation including benzyl alcohol, benzaldehyde and benzoic acid which had been reported; (3) although benzaldehyde was the primary intermediate under all RH level, amounts of the byproducts of aromatic ring oxidation were increased with the increase of RH; and (4) elevated RH increased the accumulation of benzyl alcohol but assuredly decreased the accumulation of benzaldehyde. These results suggested that (1) RH affects both the PCO rate and the PCO reaction path of toluene; (2) although methyl group oxidation is the major path, aromatic ring oxidation, which is not the expected path for the PCO of toluene, is enhanced when the RH increases; (3) apart from the role of hydroxyl radical (•OH) produced from water by TiO2, water molecule also directly takes part in the PCO process. A hypothesis has been suggested: transition species comprised of benzaldehyde, hydroxyl and water molecule exists in the PCO conversion process from benzaldehyde to benzoic acid, though the hypothesis has not been confirmed.
Keywords: Photocatalytic oxidation; Intermediates; Relative humidity (RH); TiO2/ACF; Toluene;

Two-component transparent TiO2/SiO2 and TiO2/PDMS films as efficient photocatalysts for environmental cleaning by Petra Novotná; Jiří Zita; Josef Krýsa; Vít Kalousek; Jiří Rathouský (179-185).
TiO2 films modified either with polydimethylsiloxane (PDMS) or SiO2 were prepared by a sol–gel method combined with dip-coating. TiO2/PDMS films have a lower abrasion resistance and are more hydrophobic than the TiO2/SiO2 ones. As the TiO2/PDMS films calcined at 350–450 °C exhibit developed micro-mesoporosity, they adsorb considerable amounts of methylene blue from its water solution. However, their photocatalytic activity in the decomposition of this dye is very low. On the contrary, these films are highly active in the degradation of the layers of methyl stearate. This efficiency variation is explained by the film-developed porosity. The films modified with SiO2 have very good abrasion resistance and can be easily converted by weak UV-illumination into substantially stable superhydrophilic state. Furthermore, they exhibit good photocatalytic properties in both test reactions.
Keywords: TiO2; SiO2; PDMS; Thin film; Hydrophilicity; Photoactivity;

LaMO3 (M = Mg, Ti, Fe) perovskite type oxides: Preparation, characterization and catalytic properties in methane deep oxidation by S. Petrović; A. Terlecki-Baričević; Lj. Karanović; P. Kirilov-Stefanov; M. Zdujić; V. Dondur; D. Paneva; I. Mitov; V. Rakić (186-198).
Two new series of perovskite-type oxides LaMO3 (M = Mg, Ti, Fe) with different ratio Mg/Fe (MF) and Ti/Fe (TF) in the B cation site were prepared by annealing the precursor, obtained by the mechanochemical activation (MCA) of constituent metal oxides, at 1000 °C in air. In addition, two closely related perovskites LaFeO3 (LF) and LaTi0.5Mg0.5O3 (TM (50:50)) were synthesized in the similar way. Using MCA method, perovskites were obtained in rather short time and at room temperature. The samples were characterized by X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), temperature programmed desorption of oxygen (TPD), Mössbauer spectroscopy, BET surface area measurements and tested in methane deep oxidation. According to XRPD analysis all synthesized samples are almost single perovskite phase, with trace amounts of La2O3 phase. Data of Mössbauer spectroscopy identify Fe3+ in octahedral coordination. The activity of perovskite in methane deep oxidation increases in the order TM (50:50) < MF series < TF series. Higher activity of TF samples in respect to MF with similar Fe content can be related to the structural characteristic, mainly to the presence of predominantly most labile oxygen species evidenced by TPD at lowest temperature of oxygen evaluation. In used experimental conditions, the Fe substituted perovskite are thermal stable up to the temperature of 850 °C. The stability of Fe active sites is probably the most important parameter responsible for thermal stability of perovskite, but the atomic surface composition also should be taken into account.
Keywords: Perovskite catalysts; Catalyst characterization; Methane combustion;