Mechanism of methanol conversion on ZrO<Subscript>2</Subscript> and 5% Cu/ZrO<Subscript>2</Subscript> according to in situ IR spectroscopic data

It is demonstrated by in situ IR spectroscopy that, in methanol conversion on ZrO₂ and 5% Cu/ZrO₂ catalysts, methoxy groups are present on the catalyst surface, which result from O-H or C-O bond breaking in the methanol molecule. Two types of formate complexes, localized on ZrO₂ and CuO, are also observed. The formate complexes form via the oxidative conversion of the methoxy groups. There are two types of linear methoxy groups. First-type linear methoxy groups condense with the formate complex located on CuO to yield methyl formate and then CO and H₂. Second-type methoxy groups appear as intermediate products in the formation of dimethyl ether. The main hydrogen formation reactions are the recombination of hydrogen atoms (which result from the interconversion of surface complexes) on copper clusters and the decomposition of methyl formate. The source of CO₂ in the gas phase is the formate complex, and the source of CO is methyl formate. The effect of water vapor and oxygen the surface reactions and product formation is discussed.     

Effect of the nanoparticle size of supported copper-containing catalysts on their activity in the selective oxidation of CO in an excess of H<Subscript>2</Subscript>

The catalytic properties of systems prepared by the supporting of CuO onto CeO₂, ZrO₂, and Zr_0.5Ce_0.5O₂ with particle sizes of 15–25 nm (nitrate pyrolysis (p)) and 5–6 nm (microemulsion method (me)) in the reaction of CO oxidation in an excess of H₂ were studied. In the latter case, the supports had an almost homogeneous surface and a small number of defects. The catalytic activity of (me) and (p) supports was low and almost the same, whereas the catalytic activity of CuO/(CeO₂, ZrO₂, and Zr_0.5Ce_0.5O₂)(me) samples was lower than that of CuO/(CeO₂ and ZrO₂)(p). The maximum CO conversion (∼100% at 125°C) was observed on 5% CuO/CeO₂ (p). The CO and CO₂ adsorption species on (p) and (me) catalysts were studied by TPD. Differences in the compositions of copper-containing centers on the surfaces of (p) and (me) systems were found using TPR. The nature of the active centers of CO oxidation and the effect of support crystallite size on the catalytic activity were considered.     

Structure and surface properties of ZrO<Subscript>2</Subscript>, CeO<Subscript>2</Subscript>, and Zr<Subscript>0.5</Subscript>Ce<Subscript>0.5</Subscript>O<Subscript>2</Subscript> prepared by a microemulsion method according to X-ray diffraction,TPR, and EPR data

It was established by X-ray diffraction, TPR, and EPR that microemulsion (m.e.) synthesis yields the binary oxides ZrO₂(m.e.) and CeO₂(m.e.) and the mixed oxide Zr_0.5Ce_0.5O₂(m.e.) in the form of a tetragonal, cubic, and pseudocubic phase, respectively, having crystallite sizes of 5–6 nm. The bond energy of surface oxygen in the (m.e.) samples is lower than in their analogues prepared by pyrolysis. Hydrogen oxidation on the oxides under study occurs at higher temperatures than CO oxidation. ZrO₂(m.e.) and CeO₂(m.e.) are active in O₂⁻ formation during NO + O₂ adsorption, while CeO₂ is active during CO + O₂ adsorption, too. However, its amount here is one-half to one-third its amount in the pyrolysis-prepared samples, signifying a reduced number of active sites, which are Zr⁴⁺ and Ce⁴⁺ coordinatively unsaturated cations and Me⁴⁺-O²⁻ pairs. O₂⁻ radical anions are stabilized in the coordination sphere of Zr⁴⁺ coordinatively unsaturated cations via ionic bonding, and in the sphere of Ce⁴⁺ cations, via covalent bonding. Ionic bonds are stronger than ionic-covalent bonds and do not depend on the ZrO₂ phase composition. Zr_0.5Ce_0.5O₂ is inactive in these reactions because of the strong interaction of Zr and Ce cations. It is suggested that Ce^{(4 + β)+} coordinatively unsaturated cations exist on its surface, and their acid strength is lower than that of Zr⁴⁺ and Ce⁴⁺ cations in ZrO₂ and CeO₂, according to the order ZrO₂ > CeO₂ ≥ Zr_0.5Ce_0.5O₂. Neither TPR nor adsorption of probe molecules revealed Zr cations on the surface of the mixed oxide.     

Structure and Catalytic Properties of Ceria-based Nickel Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina. The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance also depends on the crystal structure of Ni–Ce–ZrO₂. For example, nickel catalysts co-precipitated with Ce_0.8Zr_0.2O₂ having cubic phase gave synthesis gas with CH₄ conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO₂ having tetragonal phase (Ce_0.8Zr_0.2O₂) or mixed oxide phase (Ce_0.5Zr_0.5O₂) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst is attributed to a combination effect of nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂ support and the finely dispersed nano size NiO _x crystallites, resulting in the intimate contact between Ni and Ce_0.8Zr_0.2O₂ particles. The Ni/Ce–ZrO₂/θ–Al₂O₃ also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO₂ resulting in the existence of stable NiO _x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results further confirmed that NiO _x formation was more favorable than NiO or NiAl₂O₄ formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support. Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO₂/CH₄ ratio and H₂O and/or O₂ addition were also examined.     

Properties of surface compounds in methanol conversion on copper-containing catalysts based on CeO2 according to in situ IR-spectroscopic data

Formate and carbonate complexes and bridging and linear methoxy groups were detected on the surfaces of CeO₂ and 5.0% Cu/CeO₂ under the reaction conditions of methanol conversion using IR spectroscopy. The reaction products were H₂, methyl formate, CO, CO₂, and H₂O. The bridging and linear methoxy groups were the sources of formation of bi- and monodentate formate complexes, respectively. Methyl formate was formed as a result of the interaction of the linear methoxy group and the formate complex. The study demonstrated that the recombination of hydrogen atoms on copper clusters and the decomposition of methyl formate were the main reactions of hydrogen formation. Formate and carbonate complexes were the source of CO₂ formation in the gas phase, and the decomposition of methyl formate was the source of CO. It was found that the addition of water vapor to the reaction flow considerably decreased the rate of CO formation at a constant yield of hydrogen. The effects of water vapor and oxygen on the course of surface reactions and the formation of products are discussed. To explain the mechanism of methanol conversion, a scheme of surface reactions is proposed.     

ESR Study of the Formation of O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> Radical Anions on Oxidized CeO<Subscript>2</Subscript> and CeO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> Adsorbing a CO + O<Subscript>2</Subscript> Mixture

It is demonstrated by ESR measurements that O ₂ ⁻ (CO + O₂) radical anions result from CO + O₂ adsorption on the oxidized surface of CeO₂. These radical anions are stabilized in the coordination sphere of Ce⁴⁺ cations located in isolated and associated anionic vacancies. This reaction shows an activation behavior determined by CO adsorption. The variation of O ₂ ⁻ (CO + O₂) concentration with CO adsorption temperature suggests that surface carbonates and carboxylates participate in this reaction. In the (0.5– 10.0)%CeO₂/ZrO₂ system, O ₂ ⁻ forms on supported CeO₂ and is stabilized on Ce⁴⁺ and Zr⁴⁺ cations. The stability of O ₂ ⁻ -Ce⁴⁺ complexes is lower on supported CeO₂ than on unsupported CeO₂, indicating a strong interaction between the cerium cations and the support.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 423–429.Original Russian Text Copyright © 2005 by Il’ichev, Kuli-zade, Korchak.     

Promotional effect of cobalt addition on catalytic performance of Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> mixed oxide for diesel soot combustion

A series of Co-modified Ce_0.5Zr_0.5O₂ catalysts with different concentrations of Co (mass %: 0, 2, 4, 6, 8, 10) was investigated for diesel soot combustion. Ce_0.5Zr_0.5O₂ was prepared using the coprecipitation method and Co was loaded onto the oxide using the incipient wetness impregnation method. The activities of the catalysts were evaluated by thermogravimetric (TG) analysis and temperature-programmed oxidation (TPO) experiments. The results showed the soot combustion activities of the catalysts to be effectively improved by the addition of Co, 6 % Co/Ce_0.5Zr_0.5O₂ and that the 8 % Co/Ce_0.5Zr_0.5O₂ catalysts exhibited the best catalytic performance in terms of lower soot ignition temperature (T_i at 349°C) and maximal soot oxidation rate temperature (T_m at 358°C). The reasons for the improved activity were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These results revealed that the presence of Co could lower the reduction temperature due to the synergistic effect between Co and Ce, thereby improving the activity of the catalysts in soot combustion. The 6 % Co catalyst exhibited the best catalytic performance, which could be attributed to the greater amounts of Co³⁺ and surface oxygen species on the catalyst.     

Selective methanation of CO in the presence of CO<Subscript>2</Subscript> in hydrogen-containing mixtures on nickel catalysts

The screening of commercial nickel catalysts for methanation and a series of nickel catalysts supported on CeO₂, γ-Al₂O₃, and ZrO₂ in the reaction of selective CO methanation in the presence of CO₂ in hydrogen-containing mixtures (1.5 vol % CO, 20 vol % CO₂, 10 vol % H₂O, and the balance H₂) was performed at the flow rate WHSV = 26000 cm³ (g Cat)⁻¹ h⁻¹. It was found that commercial catalytic systems like NKM-2A and NKM-4A (NIAP-07-02) were insufficiently effective for the selective removal of CO to a level of <100 ppm. The most promising catalyst is 2 wt % Ni/CeO₂. This catalyst decreased the concentration of CO from 1.5 vol % to 100 ppm in the presence of 20 vol % CO₂ in the temperature range of 280–360°C at a selectivity of >40%, and it retained its activity even after contact with air. The minimum outlet CO concentration of 10 ppm at 80% selectivity on a 2 wt % Ni/CeO₂ catalyst was reached at a temperature of 300°C.     

Oxidation of ammonia using modified TiO<Subscript>2</Subscript> catalyst and UV-VIS irradiation

The impact of UV and VIS irradiation and specific nitrogen modification on a 5%Cu/5%TiO₂/SiO₂ catalyst in the course of oxidation of ammonia was investigated. It was demonstrated that both UV and VIS irradiation increased the conversion of the reactant in the reaction studied. Due to a good distribution of titanium dioxide and copper on the surface of the support, higher ammonia conversion was achieved. Physico-chemical characterisation of the catalysts studied using methods such as BET, SEM-EDS, TPD (NH₃), and TPD (CO₂) was carried out.     

Selective catalytic oxidation of ammonia into nitrogen and water vapour over transition metals modified Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript>

Copper or iron supported on commercially available oxides, such as γ-Al₂O₃, TiO₂ (anatase) and monoclinic tetragonal ZrO₂ (mt-ZrO₂) were tested as catalysts for selective catalytic oxidation of ammonia into nitrogen and water vapour (NH₃-SCO) in the low temperature range. Different commercial oxides were used in this study to determine the influence of the specific surface area, acidic nature of the support and crystalline phases as well as of the type of species and aggregation state of transition metals on the catalytic performance in selective ammonia oxidation. Copper modified oxide supports were found to be more active and selective to nitrogen than catalysts impregnated with iron. Activities of both transition metal modified samples decreased in the following order: mt-ZrO₂, TiO₂ (anatase), γ-Al₂O₃. Quantitative total ammonia conversion was achieved with the Cu/ZrO₂ catalytic system at 400°C. Characterisation techniques, e.g. H₂-temperature programmed reduction, UV-VIS-diffuse reflectance spectroscopy, suggest that easily reducible copper oxide species are important in achieving high catalytic performances at low temperatures.     

Effects of precipitants and surfactants on catalytic activity of Pd/CeO<Subscript>2</Subscript> for CO oxidation

A series of precipitants and commercial surfactants (soft templates) were employed to synthesize mesoporous/nano CeO₂ by a hydrothermal method. As-prepared CeO₂ was impregnated with palladium and employed for low-temperature catalytic oxidation of CO. It was found that both soft templates and precipitants had significant effects on the morphology, particle size, crystallinity, and porous structure of the CeO₂, having a significant effect on the surface palladium abundance, molar ratios of surface species, and catalytic activity of the final impregnated Pd/CeO₂. Using ammonia as precipitant could facilitate increased surface palladium abundance and surface molar ratios of PdO/Pd _SMSI , Ce³⁺/(Ce³⁺ + Ce⁴⁺), and O_surface/O_lattice. The catalytic activity of the final Pd/CeO₂ catalysts could be enhanced as well. The optimal P123-assisted ammonia-precipitated Pd/CeO₂ catalyst exhibited over 99% catalytic conversion of CO at 50 °C.     

In situ infrared study of formate reactivity on water–gas shift and methanol synthesis catalysts

In order to investigate the methanol synthesis reaction from CO₂/H₂, a comparative study of the reactivity of formate species on different types of catalysts and catalyst supports has been carried out. Formic acid was adsorbed on water–gas shift catalysts, Cu/ZnO/Al₂O₃ methanol synthesis catalyst and ZnO/Al₂O₃ support, Cu/ZnO/ZrO₂ and Cu/ZnO/CeO₂ methanol synthesis catalysts as well as their corresponding supports ZnO/ZrO₂ and ZnO/CeO₂. Superior reactivity and selectivity of dedicated methanol synthesis catalysts was evidenced by their behavior during the subsequent heating ramp, when these samples showed the simultaneous presence of formates and methoxy species and a higher stability of these reaction intermediates in the usual temperature range for the methanol synthesis reaction.     

Preparation and characterization of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/ZrO<Subscript>2</Subscript> catalyst for carbonation of methanol into dimethyl carbonate

A H₃PW₁₂O₄₀/ZrO₂ catalyst for effective dimethyl carbonate (DMC) formation via methanol carbonation was prepared using the sol–gel method. X-ray photoelectron spectra showed that reactive and dominant (63%) W(VI) species, in WO₃ or H₂WO₄, enhanced the catalytic performances of the supported ZrO₂. The mesoporous structure of H₃PW₁₂O₄₀/ZrO₂ was identified by nitrogen adsorption–desorption isotherms. In particular, partial sintering of catalyst particles in the duration of methanol carbonation caused a decrease in the Brunauer–Emmett–Teller surface area of the catalyst from 39 to 19 m²/g. The strong acidity of H₃PW₁₂O₄₀/ZrO₂ was confirmed by the desorption peak observed at 415 °C in NH₃ temperature-programmed desorption curve. At various reaction temperatures (T?=?110, 170, and 220 °C) and CO₂/N₂ volumetric flow rate ratios (CO₂/N₂?=?1/4, 1/7, and 1/9), the calculated catalytic performances showed that the optimal methanol conversion, DMC selectivity, and DMC yield were 4.45, 89.93, and 4.00%, respectively, when T?=?170 °C and CO₂/N₂?=?1/7. Furthermore, linear regression of the pseudo-first-order model and Arrhenius equation deduced the optimal rate constant (4.24?×?10^?3 min^?1) and activation energy (E_a?=?15.54 kJ/mol) at 170 °C with CO₂/N₂?=?1/7 which were favorable for DMC formation.     

Preparation,characterization and catalytic applications of ZrO<Subscript>2</Subscript> supported on low cost SBA-15

This work presents some applications of ZrO₂ supported over SBA-15 silica as promoter of sulfated zirconia and as support from CuO/CeO₂ catalytic system for preferential oxidation of CO to CO₂ in hydrogen rich streams, used as feed for proton exchange membrane fuel cells (PEMFC). Different amounts of ZrO₂, from 10 to 30 wt.% were incorporated. These prepared materials were characterized by powder XRD, adsorption-desorption of N₂ at 77 K, transmission and scanning electron microscopy (TEM and SEM) and X-rays photoelectron spectroscopy (XPS). The acidity was studied by thermo-programmed desorption of ammonia (NH₃-TPD). These materials were tested, after treatment with H₂SO₄, by 2-propanol dehydration and 1-butene isomerization catalytic tests. The samples were found quite good catalyst with strong acid sites, the sample with 20 wt.% of ZrO₂ being the better performing sample. Finally this material was successfully used as support for a CuO/CeO₂ system, with 6 wt.% of Cu and 20 wt.% of Ce. The resulting catalyst was tested in the preferential oxidation of CO (CO-PROX) attaining conversions close to 100% and high selectivity to CO₂.     

Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Dehydrogenation of Ethylbenzene to Styrene with Carbon Dioxide Over ZrO<Subscript>2</Subscript>-based Composite Oxide Catalysts

We have been exploring various new catalyst systems for the utilization of carbon dioxide as a soft oxidant in the catalytic dehydrogenation of ethylbenzene (EB) to styrene. The utilization of CO₂ as a soft oxidant for the commercially important catalytic dehydrogenation of EB to styrene has received enormous attention recently due to its several attractive features. This review summarizes the results of our most recent findings on zirconia-based composite oxide catalyst systems exploited for this reaction. Under this systematic and comprehensive investigation various zirconia-based composite oxide catalysts namely, TiO₂-ZrO₂, MnO₂-ZrO₂, CeO₂-ZrO₂, K₂O/TiO₂-ZrO₂, B₂O₃/TiO₂-ZrO₂ and CeO₂-ZrO₂/SBA-15 have been synthesized, characterized by various techniques and evaluated for the title reaction. Most of these composite oxide catalysts were found to exhibit very interesting physicochemical characteristics and exceptionally better catalytic properties for this reaction. As revealed by characterization results, a large number of acid–base sites with moderate strength are essential for a high conversion and product selectivity of this reaction with CO₂ as the soft oxidant.     

The catalytic performance of different promoted iron catalysts on combined supports Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for carbon dioxide hydrogenation

Global warming, fossil fuel depletion and fuel price increases have motivated scientists to search for methods for the storage and reduction of the amount of greenhouse gases, especially CO₂. The hydrogenation process has been introduced as an emerging method of CO₂ capture and convertion into value-added products. In this study, new types of catalysts are introduced for CO₂ hydrogenation and are compared based on catalytic activity and product selectivity. The physical properties of the samples are specified using BET. Iron catalysts supported on γ-Al₂O₃ with different metal promoters (X = Ni, K, Mn, Cu) are prepared through the impregnation method. Moreover, Fe–Ni catalysts supported on HZSM5-Al₂O₃ and Ce–Al₂O₃ are synthesized. Samples are reduced by pure H₂ and involved in hydrogenation reaction in a fixed bed reactor (H₂/CO₂ = 3, total pressure = 10 MPa, temperature = 523 K, GHSV = 2000, 1250 nml/min). All catalysts provide high conversion in hydrogenation reactions and the results illustrate that the selectivity of light hydrocarbons is higher than that of methane and CO. It is found that Ni has a promoting effect on the conversion fluctuations throughout the reaction with 66.13% conversion. Using combined supported catalysts leads to enhancing catalytic performance. When Fe–Ni/γ–Al₂O₃—HZSM5 is utilized, CO₂ conversion is 81.66% and the stability of the Fe–Ni catalyst supported on Al₂O₃ and Ce–Al₂O₃ furthey improves.     

Synthesis,structure, and electric properties of oxygen-deficient perovskites Ba<Subscript>3</Subscript>In<Subscript>2</Subscript>ZrO<Subscript>8</Subscript> and Ba<Subscript>4</Subscript>In<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>11</Subscript>

Perovskite phases Ba₃In₂ZrO₈ and Ba₄In₂Zr₂O₁₁ with the nominal concentration of structural oxygen vacancies 1/9 and 1/12, respectively, were synthesized by solid-phase and solution methods. X-ray diffraction showed cubic symmetry of both phases with the unit cell parameter a = 0.4193(2) and 0.4204(3) nm, respectively. The absence of superstructural lines resulted in the conclusion on statistical arrangement of oxygen vacancies. Thermogravimetry and mass spectrometry proved that both phases can reversibly absorb water from gas phase (pH₂O = 2 × 10⁻² atm) with observed correlation between the concentration of oxygen vacancies and amount of absorbed water. The total water amount was up to 0.9 mol per formula unit or, if recalculated for perovskite unit ABO₃, 0.3 and 0.23 mol H₂O, respectively. The temperature curves of coductivity in the atmosphere with various partial water vapor pressures (pH₂O = 3 × 10⁻⁵ and 2 × 10⁻² atm) showed significantly higher conductivity and lower activation energy (0.52 eV) in humid atmosphere due to proton transfer. The proton conductivity is up to 5 × 10⁻⁴ Ohm⁻¹ cm⁻¹ at 300°C for Ba₃In₂ZrO₈ specimen. IR spectrometry showed that protons in the structure exist primarily in OH-groups.     

Promoted porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH₃ decomposition because of the potential application in CO_x-free H₂ generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co₃O₄-Al₂O₃) catalysts. The Co₃O₄-Al₂O₃ catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm³ g_cat^?1 h^?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H₂-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H₂-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.