Temperature-programmed Reduction Characterization Research Articles

Remarkable enhancement of CO oxidation over Pt1/CeO2 catalysts by atomically dispersed tungsten

Ceria-supported atomically dispersed Pt is of great interest in CO oxidation due to their unique catalytic performance and high metal utilization. However, the intrinsic activity of the Pt1/CeO2 single atom catalysts may not be desirable due to the overstabilization of Pt2+ species in the CeO2 matrix. Herein, the local environment of Pt2+ species was tailored by introducing a tungsten oxide additive into the Pt1/CeO2 catalyst, achieving a dramatic improvement in catalytic performance for CO oxidation at low temperatures. The optimized catalyst with 2.5 wt% W loading achieved 100 % CO conversion at 150 °C, which was 120 °C lower than that of the unmodified Pt/CeO2 catalyst. Through in situ infrared spectroscopy and temperature-programmed reduction characterizations, as well as theoretical calculations, we concluded that the tungsten additive modulate the interactions between Pt2+ species and CeO2. Thus, the reducibility of Pt was enhanced, which facilitated the formation of catalytically active metallic Pt0 species during the reaction.

Rhenium borides (Re3B and ReB2) mechanosynthesis and their use as a catalyst for H2 production from biomass pyrolysis

In this study, we report on Re3B and ReB2 mechanosynthesis. Re3B and ReB2 are used as catalysts in H2 production by coconut shell pyrolysis from 500 to 800 °C and using 5, 10, and 20 wt % of catalyst. H2, CH4, and CO production is monitored using gas chromatography with a thermal conductivity detector. Re3B shows the highest catalytic activity for H2 production at 800 °C and 10 wt % of catalyst. Furthermore, Re3B reaches 77.4 % H2 yield at optimal conditions, the highest value reported in the literature. Re3B and ReB2 were also characterized by temperature-programmed reduction (TPR) and Fourier transform infrared spectroscopy (FTIR). We propose a scheme for molecular hydrogen formation based on TPR and FTIR characterizations, thermodynamics analysis, and H2 production.

XPS and TPR studies of 2%(Ru1/2-Sn1/2)/Al2O3catalyst synthesized by microwave techniques

X-Ray photoelectron spectroscopy (XPS) and Temperature-programmed Reduction (TPR) of 2%(Ru1/2-Sn1/2)/Al2O3 prepared by the microwave-assisted method have been studied. 2%(Ru1/2-Sn1/2)/Al2O3 have previously been evaluated as a catalyst in the reduction reaction of 4-nitrophenol. XPS and TPR studies of 2%(Ru1/2-Sn1/2)/Al2O3 was performed to confirm the metal state of Ru and Sn and reducibility of the sample, respectively. XPS data suggested that the formation of metal Ru(0) and Sn(0) in all samples. The XPS spectra of Ru 3p3/2 and Sn 3d5/2 shows binding energy peak at ∼ 461.0 ± 0.2 eV and ∼ 484,1 eV, respectively. The correlation of TPR and XPS characterization will be discussed further.

XPS and TPR studies of 2%(Ru1/2-Sn1/2)/Al2O3 catalyst synthesized by microwave techniques

X-Ray photoelectron spectroscopy (XPS) and Temperature-programmed Reduction (TPR) of 2%(Ru1/2-Sn1/2)/Al2O3 prepared by the microwave-assisted method have been studied. 2%(Ru1/2-Sn1/2)/Al2O3 have previously been evaluated as a catalyst in the reduction reaction of 4-nitrophenol. XPS and TPR studies of 2%(Ru1/2-Sn1/2)/Al2O3 was performed to confirm the metal state of Ru and Sn and reducibility of the sample, respectively. XPS data suggested that the formation of metal Ru(0) and Sn(0) in all samples. The XPS spectra of Ru 3p3/2 and Sn 3d5/2 shows binding energy peak at ∼ 461.0 ± 0.2 eV and ∼ 484,1 eV, respectively. The correlation of TPR and XPS characterization will be discussed further.

Decomposition of methane over alumina supported Fe and Ni–Fe bimetallic catalyst: Effect of preparation procedure and calcination temperature

Catalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al2O3 catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500°C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al2O3 oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results.

Preparation and characterization of Pd–Ni bimetallic catalysts for CO and C3H6 oxidation under stoichiometric conditions

Ni additive in the three-way catalyst (TWC) has been known for its high activity in H2S suppression. However, the effect of Ni on the activity of TWC in stoichiometric exhaust gas conversion is less studied. In the present work characterization of bimetallic Pd–Ni catalysts supported on γ-Al2O3 or γ-Al2O3–La2O3 for potential TWC application was performed. The catalysts were prepared by wet co-impregnation and impregnation-evaporation methods. Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectrometry (UV–vis DRS), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) techniques were employed to confirm the effect of Ni addition on the catalysts structure. XRD, TPR, and STEM characterization was employed in order to evaluate the presence of Pd–Ni interaction. The activity of the catalysts was tested in the oxidation reaction of CO and C3H6 under stoichiometric conditions. Based on the obtained results, we confirmed the structure of prepared catalysts and the effect of Pd–Ni interaction on the catalytic activity of Pd–Ni catalysts in CO and C3H6 oxidation. XRD and TPR characterization suggested that Pd and Ni are competing for the support sites. The observed competition affected Pd-support and Ni-support interactions and consequently activity. Fresh bimetallic catalysts had higher catalytic activity compared to monometallic ones due to higher active metal loading and the presence of NiO phase. It was concluded that the catalytic activity of aged bimetallic catalysts is not affected by the addition of Ni. For that reason, addition of Ni as a second metal to Pd-based catalysts for TWC reactions can be considered in the future studies.

Effect of the amount of citric acid used in the preparation of NiMo/SBA-15 catalysts on their performance in HDS of dibenzothiophene-type compounds

In the present work, NiMo catalysts supported on SBA-15 were prepared with the addition of different amounts of citric acid (CA) in the impregnation solutions. The aim of this study was to inquire into the effect of the amount of citric acid on the activity and selectivity of the NiMo/SBA-15 catalysts in deep hydrodesulfurization (HDS). Catalysts were prepared by coimpregnation of Ni and Mo species from acidic aqueous solutions containing citric acid without further adjusting the solution's pH. The amount of citric acid used in the catalyst preparation was varied from CA:Mo molar ratio 0.5 to 2.0. In addition, a reference NiMo/SBA-15 catalyst was prepared without citric acid. After the impregnation, catalysts were dried (100°C, 6h) and calcined (500°C, 4h). The prepared catalysts were characterized by nitrogen physisorption, small-angle and powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR), high resolution transmission electron microscopy (HRTEM) and tested in simultaneous HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in a batch reactor at 300°C for 8h. XRD, DRS and TPR characterizations showed that Ni and Mo oxide species were well dispersed in all catalysts prepared with CA. In contrast, a NiMoO4 crystalline phase was detected by XRD in the reference NiMo/SBA-15 catalyst prepared without citric acid. Addition of citric acid to the impregnation solutions used for the catalyst preparation also resulted in an increase in the degree of sulfidation and in the dispersion of catalytically active MoS2 phase (elemental analysis, HRTEM). In accordance with this, HDS activity of the NiMo catalysts prepared with the addition of citric acid resulted to be significantly higher than that of the reference NiMo/SBA-15 sample for both sulfur-containing compounds tested (DBT and 4,6-DMDBT). It was found that the optimum amount of citric acid, which allows achieving the highest catalytic activity, corresponds to CA:Mo molar ratio equal to 1. Further increase in the amount of citric acid resulted in a slight decrease in the HDS activity. Regarding selectivity, addition of small amounts of CA, in general, resulted in an increase of the hydrogenation ability of the NiMo/SBA-15 catalysts. However, some differences in the selectivity of the catalysts were observed with different amounts of citric acid used.

The study of bimetallic Ni–Co/cordierite catalyst for cracking of tar from biomass pyrolysis

In order to crack the tar from biomass pyrolysis, five cordierite-supported monolithic catalysts with different Ni/Co ratio were prepared by vacuum wetness impregnation. All catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), Brunauer–Emmett–Teller (BET), and scanning electron microscope (SEM). XRD and XPS characterization results show the inexistence of spinel structure such as NiAl2O4 and CoAl2O4. TPR characterization results suggest the possible formation of Ni–Co alloy. BET characterization results show that the effect of Ni/Co ratio on catalyst specific surface area is obvious. The catalytic test results show that the performance of bimetallic catalyst is better than that of monometallic catalyst. The Ni3Co1/cordierite catalyst exhibits the best catalytic performance among all bimetallic catalysts, its tar conversion and gas yield reach 96.4% and 1.21 Nm3/kg, respectively, at a weight hourly space velocity (WHSV) of 1.4 h−1.

Development of Fe–Ni/YSZ–GDC electrocatalysts for application as SOFC anodes: XRD and TPR characterization and evaluation in the ethanol steam reforming reaction

Electrocatalysts based on Fe–Ni alloys were prepared by means of modified Pechini and physical mixture methods and using on a composite of Yttria Stabilized Zirconia (YSZ) and Gadolinia-Doped Ceria (GDC) as support. The former method was based on the formation a polymeric precursor that was subsequently calcined; the later method was based on the mixture of NiO and the support. The resulting composites had 35 wt.% metal load and 65 wt.% support (70 wt.% YSZ and 30 wt.% GDC mixture) (cermets). The samples were then characterized by Temperature-Programmed Reduction (TPR) and X-Ray Diffraction (XRD) and evaluated in the ethanol steam reforming at 650 °C for 6 h in the temperature range of 300–900 °C. The XRD results showed that the bimetallic sample calcined at 800 °C formed a mixed oxide (NiFe 2O 4) with a spinel structure, which, after reduction in hydrogen, formed Ni–Fe alloys. The presence of Ni was observed to decrease the final reduction temperature of the NiFe 2O 4 species. The addition of iron to the nickel anchored to YSZ–GDC increased the hydrogen production and inhibited carbon deposition. The resulting bimetallic 30Fe5Ni sample reached an ethanol conversion of about 95% and a hydrogen yield up to 48% at 750 °C. In general, ethanol conversion and hydrogen production were independent of the metal content in the electrocatalyst. However, the substitution of nickel for iron significantly reduced carbon deposition on the electrocatalyst: 74, 31, and 9 wt.% in the 35Ni, 20Fe15Ni, and 30Fe5Ni samples, respectively.

Catalytic performance of Co-Mo-Ce-K/γ-Al2O3 catalyst for the shift reaction of CO in coke oven gas

The catalytic performance of Co-Mo-Ce-K/γ-Al2O3 catalyst for the shift reaction of CO in coke oven gas is investigated using X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The results indicate that Ce and K have a synergistic effect on promoting the catalytic activity, and the Co-Mo-Ce-K/γ-Al2O3 catalyst with 3.0 wt-% CeO2 and 6.0 wt-% K2O exhibits the highest activity. CeO2 favors Co dispersion and mainly produces an electronic effect. TPR characterization results indicate that the addition of CeO2-K2O in the Co-Mo-Ce-K/γ-Al2O3 catalyst decreases the reduction temperature of active components, and part of octahedrally coordinated Mo6+ transforms into tetrahedrally coordinated Mo6+, which has a close relationship with the catalytic activity.

Temperature-programmed reduction study on carbon-supported platinum–gold alloy catalysts

Alloy catalysts of Pt–Au/C with different Pt/Au ratios were prepared by the precipitation–deposition of metal chlorides and reduced by H 2 at 470 K. The surface composition of alloy crystallites deposited on the prepared catalysts was characterized by a technique of temperature-programmed reduction (TPR). In the characterization, O 2 was chemisorbed on the reduced catalysts and the chemisorbed O 2 was reduced by TPR. A low-temperature routine (LT) in the temperature range between 120 and 430 K was used for the TPR characterization. Monometallic catalysts of Au/C and Pt/C showed a reduction peak in the LT-TPR at reduction temperature ( T r ) = 145 and 240 K, respectively. T r from alloyed catalysts fell in the range and increased monotonously with their Pt/Au ratios. Interior Pt atoms in deposited alloy particles tended to segregate toward their surface during oxidation treatment at elevated temperatures.

TPR and XPS characterization of chromia–lanthana–zirconia catalyst prepared by impregnation and microwave plasma enhanced chemical vapour deposition methods

Chromia–lanthana–zirconia catalysts prepared by wet impregnation and microwave plasma enhanced chemical vapour deposition methods have been characterized by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The impregnation procedure requires large amounts of solvent and calcination at high temperatures producing Cr 6+ species. Unlike this, it is found that the microwave plasma enhanced chemical vapour deposition (PECVD) method predominantly produces Cr 3+ species on zirconia-based supports. Moreover, it has been shown that the dispersion of chromium species deposited on zirconia-based support by the PECVD method is higher than the dispersion of those prepared by wet impregnation. Thus, the advantages of PECVD over the impregnation method consist in this case in preventing the use of large amounts of solvent and avoiding the primary formation of poisonous Cr 6+ species as well as in enabling the deposition of chromium species with high dispersion on zirconia-based supports.

Redox properties of doped and supported copper–ceria catalysts

Copper-doped ceria catalysts feature in a variety of catalytic reactions. One important application is selective hydrogen combustion via oxygen exchange, which forms the basis of cyclic oxidative dehydrogenation. This paper describes the synthesis of monophasic (doped) and biphasic (supported) Cu-ceria catalysts, that are then characterized using a combination of temperature programmed reduction (TPR) and X-ray diffraction (XRD) methods. The catalysts are analyzed both as fresh samples and after redox cycling at 550-800 degrees C. TPR and XRD characterization clarify the role of the active sites on the catalyst surface and the copper-ceria interactions. Depending on the catalyst type, reduction occurs at approximately 110 degrees C, approximately 150 degrees C, or approximately 190 degrees C. The reduction at 110 degrees C is ascribed to highly dispersed copper species doped in the ceria lattice, and that at 190 degrees C to CuO crystallites supported on ceria. Remarkably, both types converge to the 150 degrees C feature after redox cycling. The reduction temperature of the doped catalyst increases after redox cycling, indicating that stable Cu clusters form at the surface. Conversely, the reduction temperature of the "supported" catalyst decreases after redox cycling, and the CuO crystallites disappear. With this knowledge, a copper-doped ceria catalyst is analyzed after application in selective hydrogen combustion (16 consecutive redox cycles at 550 degrees C). No CuO crystallites are observed, and the sample reduces at approximately 110 degrees C. This suggests that copper-doped ceria is the active oxygen exchange phase in selective hydrogen combustion.

Comparative Study on the Mechanisms of Partial Oxidation of Methane to Syngas Over Rhodium Supported on SiO2 and γ-Al2O3

A comparative study on the mechanisms of the partial oxidation of methane (POM) to syngas over SiO2- and γ-Al2O3-supported Rh catalysts was carried out using in situ time-resolved FTIR spectroscopy to follow the primary products of POM reaction over the catalysts. Experiments of catalytic performance evaluation and temperature-programmed reduction (TPR) characterization of the catalysts, as well as the in situ FTIR spectroscopic study using CO to probe the oxidation state of Rh species over the catalysts were performed. It was found that the direct oxidation of CH4 to syngas is the main pathway of the POM reaction over Rh/SiO2 catalysts, while the combustion--reforming mechanism is the dominant pathway of syngas formation over Rh/γ-Al2O3 catalysts. The results of TPR characterization indicate that Rh supported on γ-Al2O3 is more difficult to reduce than Rh supported on SiO2. The IR experiments of CO adsorption over Rh/SiO2 and Rh/γ-Al2O3 after the POM reaction reveal that the surface of the Rh/γ-Al2O3 catalyst contains more partially oxidized rhodium (Rh+) species as compared to the Rh/SiO2 catalyst. These results suggest that the significant difference in the mechanisms of the POM reaction over Rh/SiO2 and Rh/γ-Al2O3 catalysts can be related to the difference in the surface concentration of O2- species over the catalysts under the reaction conditions mainly due to the difference in oxygen affinity of the Rh species on the two supports.

Perturbed Angular Correlation Characterization of Indium Species on In/H-ZSM5 in the Presence of Water and Catalytic Deactivation Studies During the SCR of NOx with Methane

An In(4 wt%)-impregnated H-ZSM5 catalyst was characterized under wet and dry conditions by time-differential perturbed angular correlation (PAC) and by temperature-programmed reduction (TPR). Different indium species were quantified, correlating their structure with the catalyst deactivation due to the presence of water during the NO selective catalytic reduction (SCR) with methane. The fresh sample contains ∼60% of indium oxide and 40% of (InO)+ species at exchange sites, the latter being the active species for the reaction under study. Under wet atmosphere, hyperfine interactions determined by PAC indicate the formation of two types of In hydroxide species and the decrease of both (InO)+ and In2O3. TPR and PAC characterizations also show that deactivation is due to the decrease of (InO)+ at exchange sites to form, after water is removed, different non-active In oxide species.

Effects of the addition of titania on the thermal characterization of alumina-supported palladium

The detailed thermal characterization of Pd/TiO 2–Al 2O 3 catalysts under oxygen and hydrogen atmosphere was conducted by means of thermal gravimetric analysis/differential scanning calorimetry (TG/DSC), temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD). A simultaneous TG/DSC measurement revealed that the heat evolved during oxygen adsorption at 25 °C varied slightly with the supports and had a higher value for the smaller palladium crystallite. Hydrogen chemisorption and BET measurements revealed that the coating of Pd/Al 2O 3 catalysts with titania modified the support character to achieve a high dispersion of palladium. TPR and TPD characterizations of oxidized samples further demonstrated that the coating of Pd/Al 2O 3 catalysts with titania promoted the reduction and decomposition of PdO into palladium.

EXAFS, TDPAC and TPR characterization of PtInFerrierite: The role of surface species in the SCR of NOx with CH4

Ferrierite exchanged with In and with Pt, In (InFerrierite and PtInFerrierite) is characterized by extended X-ray absorption fine structure (EXAFS), time differential perturbed angular correlation (TDPAC) and temperature-programmed reduction (TPR). The presence of different In and Pt species is correlated with activity and selectivity during the NO selective reduction (SCR) with CH4 in the presence of excess oxygen. Both catalysts are active and selective for the said reaction. When a dry feed is used, both monometallic and bimetallic catalysts behave similarly. However, when water is present in the feed, while InFerrierite loses activity in the whole temperature range, PtInFerrierite increases its activity at temperatures above 450°C. EXAFS characterization indicates that in PtInFerrierite only a fraction of Pt is at exchange positions, the remaining fractions adopting the form of PtO2 crystals located in the outer-surface of the zeolitic structure. When this bimetallic catalyst is treated under wet reaction conditions, the formation of small metal clusters due to the reduction of PtO2 crystals occurs. Thus, the increase in activity could be due to a catalytic effect of Pt metal clusters on the NO oxidation reaction (NO+1/2O2→NO2).TDPAC characterization indicates the presence of two In species both in the monometallic and in the bimetallic catalysts: In2O3 and (InO)+Z− (In at exchange positions), the latter being the active In species for the reaction under study. TPR results also suggest the presence of highly dispersed non-crystalline In oxide species not bonded to the zeolite matrix. Neither EXAFS results nor TDPAC characterization show the presence of intermetallic Pt–In species. The results of this work prove that EXAFS and TDPAC techniques, combined with TPR and activity measurements, are powerful tools for the characterization of bimetallic catalysts.

Characterizations of alumina-supported gold with temperature-programmed reduction

Supported Au/Al 2O 3 samples of different gold loadings were prepared by the deposition-precipitation of AuCl 3 onto alumina. Prepared samples were physically characterized by techniques of atomic emission (ICP), X-ray diffraction (XRD), transmission electron microscope (TEM) and temperature-programmed reduction (TPR). According to TEM and XRD observations, the size of gold crystallites dispersed on samples freshly prepared at 300 K was ca. 8 nm. TPR characterizations of oxidized samples distinguished three kinds of reductive peaks at temperatures ca. 180, 300 and 1000 K. These peaks are attributed to reductions of gold oxides (Au sO x ) and gold chloride (Au sCl y ) on the surface of supported gold crystallites, and of gold ions (Au i) incorporated into the subsurface of alumina support, respectively. The stoichiometry x of Au sO x increased with the temperature of oxidation treatment ( T 0) and attained a peak value of 2.0 ca. T 0=600 K. Using this adsorption stoichiometry, variations in the dispersions of gold crystallites on alumina were determined. Through dispersion measurements, supported nano-crystallites of gold were found to sinter at T>673 K in both oxidative and reductive environments.

Silica-Alumina-Supported Acidic Molybdenum Catalysts - TPR and XRD Characterization

A series of silica-aluminas with controlled composition has been synthesized and used as supports for Mo oxide catalysts. X-ray diffraction (XRD) and temperature-programmed reduction (TPR) were used to study the role of support composition upon the stability of various oxidic species, including products of solid state reaction between Mo oxide and silica-alumina. In general, the reducibility of Mo increases with increasing Mo loading, regardless of support composition. For a fixed Mo loading, however, extent of reduction increases with SiO 2 content and shows a maximum at a composition SiO 2 : Al 2O 3 = 75 : 25 (wt%). Except for silica-rich catalysts, the average oxidation state of Mo does not reach below +4 at the conditions used for TPR (maximum temperature: 550°C). Most of the support compositions yield XRD-amorphous Mo oxide. Only Mo-rich and silica-rich catalysts (MoO 3 ≥ 12 wt%; SiO 2 ≥ 50 wt%) contain crystalline phases of Mo: orthorhombic MoO 3 on 100% SiO 2, and MoO 3 and Al 2(MoO 4) 3 On silica-aluminas.

Reduction and Sulfidation Properties of Iron Species in Iron-Supported Y-Zeolite by Temperature-Programmed Reduction and Sulfiding

Temperature-programmed reduction (TPR) and temperature-programmed sulfiding (TPS) were used to characterize reduction and sulfiding properties of Fe-exchanged Y-zeolites and Fe-treated Y-zeolites, which were prepared by treating NH4Y-zeolite with an aqueous ferric nitrate solution (Fe-treatment). By considering their unique TPR and TPS patterns, it was confirmed that the Fe2+-species in the Fe-exchanged Y-zeolites are stabilized inside the sodalite cages and the hexagonal prisms. On the basis of the TPR and TPS characterizations, it was demonstrated that three types of the Fe-species are present in the Fe-treated Y-zeolites: ion-exchanged species, small Fe oxide clusters, and Fe oxide without interaction with the zeolite framework (including aggregated ferric oxide), the proportion of which is dependent on the extent of the Fe-treatment. Prolonged Fe-treatment weakens the interaction between the Fe-species and the framework oxygen atoms by hydrolysis, and leads to the aggregation of the Fe oxides and to the formation of bulk ferric oxide. The small Fe-oxide clusters, which are probably situated inside the supercages through a coordination with the framework oxygen atoms, are responsible for the high activity for toluene disproportionation in the presence of H2S.