TPR Analysis Research Articles

Nitrate removal in drinking waters: the effect of tin oxides in the catalytic hydrogenation of nitrate by Pd/SnO2 catalysts

The preparation of some new Pd-Cu and Pd only catalysts dispersed on ZrO2 and SnO2 is reported. All samples are characterized by BET, TPR and powder XRD analysis. The hydrogenation of 100ppm nitrate solutions shows significant differences depending on the pH control method. The use of CO2 in the gas feed allows to reduce the formation of ammonia. Pd/SnO2 catalysts represent the best combination between activity and selectivity and both can be improved by decreasing the reduction temperature of the catalyst. These results suggest a possible role for SnOx in the control of the activity and selectivity of the reaction.

Partial Oxidation of Methane to Syngas over Calcined Ni–Mg/Al Layered Double Hydroxides

The catalytic partial oxidation of CH4 to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH4 into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl2O4 spinel phase had a positive effect on the stability of the catalyst.

La, Ca and Fe oxide perovskites: preparation, characterization and catalytic properties for methane combustion

La1−xCaxFeO3 (x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K have been investigated as catalysts for methane combustion. The formation of the perovskite structure has been shown by X-ray diffraction (XRD) for all samples. The surface area (SA) values are in the range 3–6m2g−1 for the samples up to x=0.4, whereas SA is 0.7m2g−1 for the specimen with x=0.5. The atomic susceptibility increases with increasing in Ca content. The Fe4+/Fetotal ratio has been determined by both redox titration and TPR analysis. The amount of Fe4+ enhances with Ca substitution but the Fe4+/Ca2+ ratio is quite constant giving rise to an increasing formation of oxygen vacancies to preserve charge neutrality. All perovskites show a similar intrinsic activity in CH4 combustion with activation energy, Ea, of about 23kcalmol−1. A slightly lower value of Ea is shown by LaFeO3 which, in contrast with Ca substituted samples, exhibits a small cationic defectivity. Methane reaction order lower than one was found for all catalysts.

Yttria-stabilized zirconia supported platinum catalysts (Pt/YSZs) for CH 4/CO 2 reforming

Yttria-stabilized zirconia (YSZs) samples with various amounts of yttrium were prepared, characterized, and used as supports for preparing Pt/YSZ catalysts. CH 4/CO 2 reforming over the Pt/YSZ catalysts was examined and compared with the results over Pt/Al 2O 3 and Pt/SiO 2 catalysts. Analysis of TPR revealed that the reduction temperature range of the Pt/YSZ catalysts was much lower than that of the Pt/Al 2O 3 and Pt/SiO 2 catalysts. For CH 4/CO 2 reforming at 600°C, the Pt/YSZ catalysts showed a higher steady state conversion and significantly better stability than the Pt/Al 2O 3 and Pt/SiO 2 catalysts. These results were attributed to the enhancing of adsorption, activation and dissociation of CO 2 on the YSZ. The optimum dosage of yttrium in YSZ for the CH 4/CO 2 reforming reaction was 9.8 mol% (Y/(Zr+Y)). Additionally, YSZ(9.8) could be homogeneously spread on the SiO 2 and was more stable than the YSZ(9.8) for the CH 4/CO 2 reforming at temperatures above 700°C.

Catalytic activity and stability of a chromium containing silicate in liquid phase cyclohexane oxidation

A chromium containing silicate has been prepared by an acid-catalyzed sol–gel process. The material was characterized by FTIR, UV–VIS and EPR spectroscopy as well as TPR, XRD and XRF analyses. The silicate is an efficient catalyst for the oxidation of cyclohexane with tert-butyl hydroperoxide. Leaching studies showed that catalysis is at least in part due to traces of Cr leached into the homogeneous phase. Weakly bound Cr species can be removed by soxhlet extraction, yielding a catalyst which is remarkably leaching resistant. The catalyst can be used at least four times without detectable loss of metal.

Particle size effect in the catalytic hydrogenation of 2,4-dinitrotoluene over Pd/C catalysts

The liquid phase hydrogenation of 2,4-dinitrotoluene (2,4-DNT) to 2,4-diaminotoluene (2,4-DAT) has been studied over palladium supported on carbon. Catalytic activity and selectivity to the intermediate products were found to depend on the metal particle size. The larger metal particles were the most active and selective towards the formation of the 2,4-nitrohydroxyaminotoluene isomers. The catalysts have been characterized by TPR, XRD, TEM and CO chemisorption. TPR analysis has shown that no formation of a palladium β-hydride phase occurs on these systems irrespectively of the metal particle size. This apparently anomalous behavior has been attributed to the contamination of the Pd metal particles by impurities and/or C atoms migrating from the support. On the basis of the reported results the relationships between the catalytic activity and the metal particle size in the hydrogenation of 2,4-DNT is discussed.

Surface properties and catalytic performance for ethane combustion of La 1− xK xMnO 3+ δ perovskites

The influence of K substitution in LaMnO 3 perovskite on the surface properties and catalytic oxidation of ethane has been studied. La 1− x K x MnO 3+ δ perovskites ( x=0.05, 0.10, 0.15, 0.20 and 0.25) with BET surface area of 20–26 m 2 g −1 have been prepared by the freeze-drying method and characterized by X-ray diffraction patterns (XRD), TPR, TPD and XPS. The XRD analyses showed the presence of a single crystalline phase ( x≤0.15) with the linear increase of the lattice parameter corroborating the incorporation of potassium in the perovskite structure. The XPS studies revealed an enrichment of the perovskite surface with potassium accompanied by an increase in the surface Mn 4+/Mn 3+ ratio. The TPR and chemical analyses suggested the presence of an oxygen non-stoichiometry ( δ) of +0.15 for LaMnO 3 which decreases to −0.04 for La 0.85K 0.15MnO 3. Oxygen temperature programmed desorption experiments showed similar results with the amount of β oxygen desorption decreasing in the presence of potassium in the perovskite structure. The catalytic activity for the total oxidation of ethane decreased for K containing perovskite and was closely related to the oxygen non-stoichiometry ( δ). The effect of oxygen partial pressure and temperature suggests the predominance of an intrafacial mechanism at higher temperature with a possible contribution of the suprafacial reaction at lower temperatures.

Effects of Cu over Pd based catalysts supported on silica or niobia

Palladium and palladium-copper catalysts supported on silica and niobia were characterized by H2 chemisorption and H2-O2 titration. Systems over silica were also analyzed by transmission electron microscopy and EXAFS. The metallic dispersion decreased from 20% to 7% when the content of Pd was increased from 0.5wt.-% to 3wt.-% in monometallic catalysts. The addition of 3 wt.-% Cu to obtain Pd-Cu catalysts caused a remarkable capacity loss of hydrogen chemisorption. TPR analysis suggested an interaction between the two metals and EXAFS characterization of the catalyst supported on silica confirmed the formation of Pd-Cu alloy. Pd/Nb2O5 catalysts showed turnover numbers higher than those obtained with the Pd/SiO2 systems in the cyclohexane dehydrogenation. However, the bimetallic catalysts showed very low turnover numbers.

Active sites in Cu/ZnO/ZrO 2 catalysts for methanol synthesis from CO/H 2

Among various Cu/ZnO/ZrO 2 catalysts with the Cu/Zn ratio of 3/7, the one with 15 wt.% of ZrO 2 obtains the best activity for methanol synthesis by hydrogenation of CO. The TPR, TPO and XPS analyses reveal that a new copper oxide phase is formed in the calcined Cu/ZnO/ZrO 2 catalysts by the dissolution of zirconium ions in copper oxide. In addition, the Cu/ZnO/ZrO 2 catalyst with 15 wt.% of ZrO 2 turns out to contain the largest amount of the new copper oxide phase. When the Cu/ZnO/ZrO 2 catalysts is reduced, the Cu 2+ species present in the ZrO 2 lattice is transformed to Cu + species. This leads to the speculation that the addition of ZrO 2 to Cu/ZnO catalysts gives rise to the formation of Cu + species, which is related to the methanol synthesis activity of Cu/ZnO/ZrO 2 catalyst in addition to Cu metal particles. Consequently, the ratio of Cu +/Cu 0 is an important factor for the specific activity of Cu/ZnO/ZrO 2 catalyst for methanol synthesis.

Effect of siderite in coal on reductive pyrolytic analyses

The effect of the presence of siderite (FeCO 3) in coal on the atmospheric pressure–temperature programmed reduction (AP–TPR) analysis of coal is studied. Siderite is added to demineralised Maritza Iztok (lignite) and raw Nowy Wirek (high volatile bituminous) coal before analysis. Results show an extra troilite FeS peak in the AP–TPR profiles for both siderite doped coals. The mechanism of H 2S capture by siderite is discussed on the base of a model reaction. Additionally, the formation of troilite from the pyrite present in the initial coal during the AP–TPR experiment was monitored by scanning electron microscopy with an energy dispersive X-ray analyser (SEM–EDX). During AP–TPR analysis the evolving H 2S is captured by FeO or FeCO 3 and FeS is formed. These phenomena disturb the AP–TPR profiles as well as the sulphur recovery.

TPR and XPS study of cobalt–copper mixed oxide catalysts: evidence of a strong Co–Cu interaction

In this work the results of a TPR and XPS investigation of CoxOy–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N2 at 723 K for 24 h of single‐phase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co2+[Co3]2O4 (Co3O4) spinel phase. The copper‐containing catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co2+[Co3+]2O4, Co 1-x 2+ Cu x 2+ [Co3+]2O4 and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co2+, Co3+ and Cu2+ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co3O4 and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N2 formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu+Co3+O2 compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO2 phase was the main component. A further addition of copper led to the formation of CuCoO2 and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N2‐calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction.

CO and NO Adsorption on Alumina–Pd–Mo Catalysts: Effect of the Precursor Salts

The effect of the palladium precursor on the CO and NO adsorption capacity of Pd–MoO3/Al2O3 catalysts was studied. TPR and IR analysis showed that the palladium addition promoted the reduction of Mo6+ to Mo4+. The presence of a higher amount of molybdenum oxide partially reduced improved the NO dissociation to N2 and N2O on Pd–Mo/Al2O3 catalysts. This behavior was attributed to the formation of a lower fraction of inactive adsorbed nitrogen species on molybdenum oxide partially reduced. The catalytic behavior of the Pd–Mo/Al2O3 catalysts on the NO+CO reaction could be explained by a bifunctional mechanism. After adsorption and dissociation of NO on Mo4+, the oxygen dissociated is transferred to the Pd. The CO adsorbed on the Pd surface reacts to CO2.

Catalytic activity of chromium spinels in SCR of NO with NH3

Series of chromium spinels MCr2O4 (M=Mg, Zn, Fe, Co, Ni, Cu, Mn) were tested in the selective catalytic reduction (SCR) of NO with NH3. Catalytic activity and selectivity to N2O depend on the nature of the divalent metal M. The studies by TPR, XPS and chemical analysis lead to the conclusion that the surface layer of all chromium spinels decomposes to simple oxide species containing M2+/M3+ and Cr3+/Cr6+ redox systems. An increase in the oxidation potential of the redox system is accompanied by a decrease in the selectivity to N2O in agreement with the mechanism of the reaction proposed by the Niiyma group.

Functional analysis of Tpr: identification of nuclear pore complex association and nuclear localization domains and a role in mRNA export.

Tpr is a 270-kD coiled-coil protein localized to intranuclear filaments of the nuclear pore complex (NPC). The mechanism by which Tpr contributes to the structure and function of the nuclear pore is currently unknown. To gain insight into Tpr function, we expressed the full-length protein and several subdomains in mammalian cell lines and examined their effects on nuclear pore function. Through this analysis, we identified an NH2-terminal domain that was sufficient for association with the nucleoplasmic aspect of the NPC. In addition, we unexpectedly found that the acidic COOH terminus was efficiently transported into the nuclear interior, an event that was apparently mediated by a putative nuclear localization sequence. Ectopic expression of the full-length Tpr caused a dramatic accumulation of poly(A)+ RNA within the nucleus. Similar results were observed with domains that localized to the NPC and the nuclear interior. In contrast, expression of these proteins did not appear to affect nuclear import. These data are consistent with a model in which Tpr is tethered to intranuclear filaments of the NPC by its coiled coil domain leaving the acidic COOH terminus free to interact with soluble transport factors and mediate export of macromolecules from the nucleus.

Hydrogenation of Fatty Esters over Ruthenium–Tin Catalysts; Characterization and Identification of Active Centers

The selective hydrogenation of methyl oleate into oleyl alcohol was performed over RuSn/alumina catalysts. A maximum yield of unsaturated alcohol was obtained for a bulk atomic ratio to Sn/Ru=4. The side reaction of the transesterification between methyl oleate and oleyl alcohol leading to oleyl oleate was strongly decreased. The ruthenium–tin catalysts prereduced with NaBH4have been characterized by TPR and XPS analysis. The addition of tin increased the content of Ru° on the catalyst surface without modification of the total Ru content. When the catalysts were reduced with NaBH4, a decrease of the tin and ruthenium contents on the surface was observed. On the catalyst surface were found two separate tin oxide species which differed in the oxidation state of tin. The proportion and the repartition of each species was a function of the total tin content. Over such catalysts, the reaction scheme involved three steps: (1) the hydrogenation of the methyl oleate into the oleyl alcohol, (2) the transesterification reaction between the methyl oleate and the oleyl alcohol with the formation of the heavy oleyl oleate ester, (3) the hydrogenation of this heavy ester into oleyl alcohol. The first and the third steps could involve mixed ruthenium–tin sites while the second step could require tin species without an interaction with ruthenium. If it is assumed that the rate determining step is the oleyl oleate hydrogenation, the results of this study show that active centers corresponding to a stoechiometry Ru/SnOx=2 could be involved in this reaction. The activation of esters (methyl oleate and oleyl oleate) would occur via a hemiacetal intermediate over these mixed sites where the more reduced tin species could be close to the ruthenium.

Unsupported MoO 3Fe 2O 3 catalysts: characterization and activity during 2-propanol decomposition

The catalytic decomposition of 2-propanol (2-PrOH) was studied as probe reaction, in the gas phase, over unsupported MoO 3Fe 2O 3 mixed catalysts. The samples were prepared by mixing MoO 3 (as ammonium heptamolybdate) with different x mol% Fe 2O 3 (as ferric nitrate) and calcined at 500°C in air for 5 h. All catalysts were characterized by TPR, IR, XRD and XPS analyses. The surface area of these samples were determined using the BET method. Also, the acidity and the basicity of all catalysts were estimated thermogravimetrically using the adsorption of pyridine and formic acid as probe molecules. The catalytic decomposition of 2-PrOH was studied over the catalysts in the temperature range of 150–260°C. A correlation between the catalytic activity and the acidity or the basicity of these catalysts has been made. The activation energies for both propene and acetone formation, over MoO 3Fe 2O 3 catalysts, were calculated.

96/05751 Coal maceral separation using column flotation

The effect of the presence of siderite (FeCO3) in coal on the atmospheric pressure–temperature programmed reduction (AP–TPR) analysis of coal is studied. Siderite is added to demineralised Maritza Iztok (lignite) and raw Nowy Wirek (high volatile bituminous) coal before analysis. Results show an extra troilite FeS peak in the AP–TPR profiles for both siderite doped coals. The mechanism of H2S capture by siderite is discussed on the base of a model reaction. Additionally, the formation of troilite from the pyrite present in the initial coal during the AP–TPR experiment was monitored by scanning electron microscopy with an energy dispersive X-ray analyser (SEM–EDX). During AP–TPR analysis the evolving H2S is captured by FeO or FeCO3 and FeS is formed. These phenomena disturb the AP–TPR profiles as well as the sulphur recovery.

Dehydrogenation and aromatization of methane in the absence of oxygen on Mo/HZSM-5 catalysts before and after NH4OH extraction

Mo/HZSM-5 catalysts show good catalytic reactivity in the absence of oxygen for the dehydrogenation and aromatization of methane at 973 K. The active Mo species were investigated by combining catalytic studies on Mo/HZSM-5 catalysts before and after NH4OH extraction with XRD, BET, NH3-TPD and TPR analysis. The XRD patterns show that Mo species are well dispersed on the zeolite surface. The specific surface areas decrease with increasing Mo loading but they can be restored to a large extent by NH4OH extraction. NH3-TPD results suggest that the Mo species prefer to deposit on the strong acid sites of HZSM-5 zeolite. TPR profiles show that there is a kind of Mo species which is easily reduced. No TPR peaks could be obviously observed if the Mo/ HZSM-5 catalysts were extracted by NH4OH solution. The results of NH4OH extraction experiment and other relevant characterization studies suggest that there are several kinds of Mo species deposited on the surface. By referring to the Mo species on Al2O3 supported MoO3 samples, we propose that the dissolvable Mo species in NH4OH solution are MoO3 crystallites and their aggregates in octahedral coordination, while the unsoluble Mo species mainly are Al2(MoO4)3 and MoO 4 2− in tetrahedrally coordinated form. The catalytic performance of Mo/HZSM-5 catalysts before and after NH4OH extraction illustrates that Mo species in small MoO3 crystallites with octahedral coordination form are active for methane activation in the absence of oxygen on Mo/HZSM-5 catalysts, while Mo species in tetrahedrally coordinated form is less active for the reaction.

High pressure reaction of methanol with CO or CO + H 2 catalyzed by sulfided [formula omitted

The reaction of methanol with CO or CO + H 2 has been carried out over various carbon supported CoMo sulfided catalysts at pressures up to 75 atm and temperatures of 250 and 300°C. Methyl acetate was the main product in the reaction of methanol with CO. When the reaction was carried out at high-temperature conditions, high pressures of MeOH and CO prevented changes in selectivity by aggregation, as shown by TPR analysis. Sulfided CoMo C catalysts were inactive for the hydrogenation of CO to methanol. However, the reaction of MeOH with CO + H 2 resulted in significant ethanol selectivity, especially at 300°C. Ethanol is probably formed by hydrogenation of both acetaldehyde and methyl acetate, the latter taking place mainly at 300°C.

Heteropolyanions as Redox Components in Heterogeneous Wacker Oxidation Catalysts

Heteropolyanions (HPAs) of the Keggin type have been successfully applied as redox components in heterogeneous Wacker catalysts. The catalysts consist of a silica support covered with a layer of HPA of the series H3+nPVnMo12−nO40 on which a submonolayer of palladium sulfate is deposited. The initial butanone yield in the oxidation of 1-butene at 343 K is approximately 0.10 g butanone per gram of catalyst per hour. The steady-state activity is, however, a factor of 10 lower due to the slow reoxidation of reduced HPA. The rate of reoxidation and hence the steady-state activity increases with increasing number (n) of vanadium atoms per Keggin unit and when the protons of the HPA are replaced by Cu2+ or by Ni2+. Even higher activity is obtained with palladium salts of heteropolyacids. In these palladium salts the palladium reaction centre and the redox component are combined in one complex. The butanone selectivity of the catalysts with n > 0 is high, viz. >95%, and increases with increasing values of n to more than 98%. The butanone selectivity also increases when the protons are exchanged for metal cations, such as Cu2+, Ni2+, Pd2+, or Cs+. The stability of the Keggin units under reaction conditions is high. Under Wacker oxidation conditions the HPAs are partly reduced, but DRIFT and ESR spectroscopy and TPR analysis of used catalysts show that the Keggin structure remains intact. Reoxidation of the reduced HPAs is, however, slow under reaction conditions.