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Abstract: High catalytic activity for selective catalytic reduction of NO x with dimethyl ether and methanol (DME- and methanol-SCR) has been found over a γ-alumina catalyst. The surface species involved in the DME-SCR reaction were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with mass spectrometry and compared to the corresponding species observed during methanol-SCR. Dimethyl ether adsorbs mainly as methoxy groups (h name="sbnd" />CH3) on the catalyst surface, while methanol adsorbs as methoxy groups and molecularly. With increasing temperature, DME desorbs in two steps, whereas methanol desorbs first as methanol and at higher temperatures as DME. At higher temperatures, the two reducing agents display similar DRIFTS spectra showing first formaldehyde-like species and then formates on the surface. In the presence of NO or NO2, reactions between NO x species and carbon-containing species occur. Formohydroxamic acid (CHOorms isocyanates (NCO), and both are observed at temperatures relevant for DME-SCR. Since these species are likely intermediates for hydrocarbon-SCR over Ag/Al2O3, a partly similar reaction mechanism may be operational for DME-SCR over γ-Al2O3 despite the fact that Ag/Al2O3 does not catalyze DME-SCR efficiently. The difference is thus due to the reaction steps leading to the formation of formohydroxamic acid that with DME follow a more efficient route over γ-Al2O3 than over Ag/Al2O3. [Copyright &y& Elsevier]

Abstract: Recently, we have found that forming a slurry by mixing Ca oxide with biodiesel (approximately 10–15g of biodiesel per gram of Ca oxide) results both in protection against poisoning by atmospheric CO2 and H2O and, when the slurry is used as a catalyst, in a remarkable increase in reaction rate [M. Lopez Granados et al., Energy Fuel 23 (2009) 2259–2263]. By conducting catalytic tests and DRIFT studies with either sunflower oil or model compounds revealed that the presence of minute amounts of monoglycerides (MG) and/or diglycerides (DG) in the biodiesel were the reason for the reaction rate promotion. To observe this effect, the Ca oxide–biodiesel slurry must be pretreated with methanol for a few minutes before proceeding with the transesterification reaction. The DRIFT studies demonstrated that the transesterification of MG and DG during the pretreatment with methanol results in the releasing of glycerol, which then reacts with the catalyst surface, resulting in the formation of very active surface Ca glyceroxide species. In view of this information, it was also demonstrated that the two-step procedure of mixing biodiesel with the catalyst and then carrying out methanol pretreatment could be substituted with pretreatment of the Ca oxide with methanol containing a few milligrams of glycerol per gram of Ca oxide before proceeding with the reaction. In this latter case, the slurry was not required. The DRIFT studies demonstrated that this simpler pretreatment also resulted in the formation of very active surface Ca glyceroxide species. [Copyright &y& Elsevier]

Abstract: Complexes of bivalent iron stabilized in the FeZSM-5 zeolite matrix (α-sites) are known to be able to decompose nitrous oxide stoichiometrically to form oxygen anion radicals, O−, bound to iron (α-oxygen), Similar to O− radicals on V and Mo oxides, α-oxygen is highly reactive in respect to CO, H2, methane and other hydrocarbons. It participates in catalytic oxidation of benzene to phenol by nitrous oxide, providing selectivity close to 100%. In this work, adsorption measurements, IR spectroscopy, TPD, and isotope methods were used to describe an earlier unknown reaction of O− species with water, which proceeds at 5–200 °C via the hydrogen abstraction mechanism according to the equation The reaction leads to the hydroxyl groups formed on α-sites, and equivalent amount of O2 evolves into the gas phase from water. Desorption of the hydroxyl groups occurs at above 400 °C via their recombination into water and dioxygen, resulting in the reactivation of α-sites, High sensitivity of α-oxygen to water admixtures may be an important factor explaining some contradictory results reported in the literature on the behavior of α-oxygen. Because α-oxygen is a typical representative of anion radicals O−, this reaction may be relevant not only to the conventional oxidation catalysis over zeolites and metal oxides, but also to photocatalytic processes, where formation of O− is well documented. [Copyright &y& Elsevier]

Abstract: The excellent selectivity and activity of ruthenium-hydroxyapatite {RuHAp, HAp=Ca10(PO4)6(OH)2} in the aerobic oxidation of alcohols has been attributed to isolated, monomeric Ru3+ species as the active sites. Here we reinvestigated these catalysts by a DRIFT study of CO adsorption and by electron microscopy (STEM) combined with EDX analysis. The study revealed the presence of two major species: isolated Ru3+ ions and hydrated Ru3+-oxide particles. The latter structure has high redox activity; it is easily oxidized with oxygen to RuO2 and reduced by hydrogen or CO at ambient conditions. The amount of this phase in the catalysts correlates well with the alcohol oxidation activity in the liquid phase at close to ambient conditions. In contrast, the redox activity of isolated Ru3+ ions is significantly lower (or they might be completely inactive). These species may correspond to adsorbed Ru3+ ions, ion-exchanged Ru3+ at the outer surface of HAp, or Ru3+ ions in Ru-phosphate formed by a dissolution–redeposition process from HAp. Our final conclusion is that in RuHAp, the real active sites are small hydrated Ru3+-oxide nanoparticles (1–2 nm) located on the surface of HAp. Application of a low RuCl3 concentration and a short contact time between HAp and the aqueous RuCl3 solution during catalyst preparation help maximize the fraction of the Ru3+-oxide phase and thus the catalytic activity. [Copyright &y& Elsevier]

Abstract: The oxidation of reduced Ga species in ZSM-5 zeolite modified via anchoring of trimethyl gallium or by incipient wetness impregnation with a solution of gallium nitrate was studied. Reduction of such materials in hydrogen and evacuation at high temperature resulted in quantitative replacement of the Brønsted acidic protons by Ga+ ions. However, the extent of dealumination of the material prepared by incipient wetness impregnation was higher. Oxidation of univalent gallium species by nitrous oxide at 673 K by either preparation method led to the quantitative formation of charge-compensating [Ga3+(O2−)]+ fragments. Ga+ ions can also be oxidized at 573 K by water vapor, whereupon approximately 25% of the Ga+ ions are transformed into [GaO]+ with concomitant release of molecular hydrogen. Dissociative chemisorption of molecular hydrogen via oxidative addition of hydrogen atoms to Ga+ cations at 773 K resulted in the formation of gallium dihydride species, which are very stable and are decomposed only in vacuum above 673 K. Oxidation of such [Ga3+(H−)2]+ cations by N2O at 573 K gave positively charged [Ga3+(H−)(OH)−]+ species. At higher temperature (673 K), the latter are further oxidized by nitrous oxide, giving neutral GaOOH species and Brønsted acidic protons. The similarity of infrared spectra of ethane adsorbed on Ga/ZSM-5 and HZSM-5 at 298 K indicates weak polarization of ethane molecules by Ga+ cations. However, oxidative addition of ethane at 523 K led to the formation of [Ga3+(H−)(C2 )]+ species. Above 573 K the grafted ethyl fragments decomposed to gallium hydride species and ethylene. Indications were also found for subsequent oligomerization and aromatization of the resulting olefin. [Copyright &y& Elsevier]

Abstract: Sulfated zirconia, unpromoted or promoted with either 2 wt% iron or manganese, was investigated by in situ diffuse reflectance IR spectroscopy during activation, n-butane isomerization (323–378 K, 1–5 kPa n-butane), and regeneration. During activation at 773 K in N2 or O2, more than 95% of the adsorbed water was removed, and comparison of the resulting pattern of sulfur–oxygen vibrations with DFT calculations (A. Hofmann and J. Sauer, J. Phys. Chem. B 108 (2004) 14652) suggests as a major surface species. All catalysts underwent an induction period before maximum rates were measured, which at 1 kPa n-butane were 350 and 180 μmol g−1 h−1 for the Fe- or Mn-promoted catalyst (323 K) and 5 μmol g−1 h−1 for sulfated zirconia (358 K). During isomerization several bands increased in the range of 1700–1600 cm−1; the growth of a band at 1600 cm−1 was restricted to the period of increasing catalytic activity. The rate of isomerization was linearly correlated with the total area increase of the bands in this region, indicating that the absorbing species are either active surface intermediates or side products (possibly water) formed in an amount proportional to the active surface species. The rate per such species was much higher in the presence of Mn; that is, promoters facilitate reaction steps after the initial alkane activation. The promoted materials deactivated within hours under the applied conditions, but complete recovery of the spectral and catalytic properties of Mn-promoted sulfated zirconia was possible through regeneration in O2 at 773 K. Attempts to regenerate in N2 produced unsaturated surface species absorbing at 1532 and 1465 cm−1. [Copyright &y& Elsevier]

Abstract: CuMgAl ternary hydrotalcites with a (Cu+Mg)/Al atomic ratio of 3.0 and a Cu/Mg atomic ratio of 5.0, 3.0, 1.0, 0.33, and 0.2 were synthesized by coprecipitation under low supersaturation. Powder X-ray diffraction (PXRD) of all of the samples showed the pattern characteristic of hydrotalcite without any detectable impurity phases, with the crystalline order, especially in the ab plane, improving with an increase in magnesium concentration. In situ PXRD studies revealed varying phase evolution processes depending on the concentration of magnesium; this observation was well complemented by in situ diffuse reflectance infrared Fourier transform (DRIFT) measurements. The thermal stability of these materials also improved with an increase in magnesium concentration, as indicated by TG-DTA-EGA measurements. However, a characteristic endotherm was noted at temperatures around 870 K accompanied by the evolution of CO2, the intensity of which increased with an increase in copper concentration. Catechol (CAT) and hydroquinone (HQ) were the main products noted in the hydroxylation of phenol over these materials, with H2O2 as oxidant and H2O as solvent. Variation of the substrate:catalyst mass ratio (10–500) showed that the activity passes through a maximum for a ratio of 100. The influence of reaction time indicated that the reaction was nearly complete in less than 60 min. Activity was enhanced by an increase in the concentration of copper, whereas the normalized activity (activity per unit copper concentration) showed an opposite trend. The structure–activity relationship of these samples, obtained through scanning electron microscopy, N2 adsorption measurements, X-ray photoelectron spectroscopy, and cyclic temperature-programmed reduction–oxidation measurements, corroborated such activity variations. [Copyright &y& Elsevier]

Reduction in hydrogen at 773 K of gallium-modified HZSM-5 zeolite prepared by incipient wetness impregnation results in complete substitution of acidic hydroxyl groups. The modification of the zeolite with gallium suppresses dealumination of the hydrogen form due to substitution of protons by gallium species. When the reduction at 773 K is followed by evacuation, coordinatively unsaturated Ga+ ions are formed. These species can be reversibly oxidized by nitrous oxide at 673 K. Alternatively, these Ga+ ions adsorb molecular hydrogen at lower temperatures resulting in several types of hydride species. The latter species are completely decomposed only in vacuum at relatively high temperatures (773 K). We propose that the oxidation of gallium upon cooling of reduced samples to room temperature in hydrogen can be attributed to an oxidative addition of H2 resulting in the formation of gallium dihydrides. [Copyright &y& Elsevier]