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This work presents results on CO2 hydrogenation to dimethyl ether (DME) over bifunctional catalysts consisting of In2O3, supported on natural clay halloysite nanotubes (HNT), and HNT modified with Al-MCM-41 silica arrays. The catalysts were characterized by TEM, STEM, EDX-mapping, NH3-TPD, XRD, low-temperature nitrogen adsorption, TPO, and H2-TPR techniques. Catalytic properties of In2O3/HNT and In2O3/Al-MCM-41/HNT in the CO2 hydrogenation to DME were investigated in a fixed-bed continuous flow stainless steel reactor at 10–40 atm, in the temperature range of 200–300°C, at GHSV = 12,000 h−1 and molar ratio of H2:CO2 = 3:1. The best catalyst for CO2 hydrogenation was In2O3/Al-MCM-41/HNT that provided DME production rate 0.15 gDME·(gcat·h)−1 with DME selectivity 53% and at 40 bar, GHSV = 12,000 h−1, and T = 250°C. It was shown that In2O3/Al-MCM-41/HNT exhibited stable operation for at least 40 h on stream.

[M(NH3)4]A (M=Pt, Pd; A=CrO4, Cr2O7) and [Pt(NH3)4(NO2)(Cr2O7)]NO3 complex salts were synthesized and characterized by a number of physicochemical methods of analysis (IR, single‐crystal and powder XRD, and simultaneous thermogravimetry and differential scanning calorimetry with evolved gas analysis mass spectrometry). Thermolysis of the salts obtained in a hydrogen atmosphere proceeds with the partial reduction of chromium to a metallic state and the formation of MxCr1−x (M=Pt, Pd) metal solid solution with a chromium content of up to 22 at % and chromium(III) oxide. The thermal decomposition of salts in an inert and oxidizing atmosphere passes through the formation stage of the MCrO2 phase with the delafossite structure followed by its subsequent decomposition into chromium(III) oxide and noble metal. Nanosized Pt−Cr2O3 and Pd−Cr2O3 composites obtained by the thermolysis of precursor salts in air at 500 °C and being held at this temperature for 1 h showed a high catalytic activity in the CO total oxidation (TOX) and preferential oxidation in the excess of hydrogen (PROX) processes compared with that of monometallic Pt and Pd powders. [ABSTRACT FROM AUTHOR]

Structured composite Ni(Clx)/CeO2/η‐Al2O3/FeCrAl catalysts are developed for the reaction of preferential methanation of carbon monoxide in the presence of carbon dioxide. The use of a FeCrAl alloy wire mesh as a support for Ni(Cl)/CeO2 allows preparation of a heat‐conducting catalyst that is similar in performance and physical‐chemical properties to the highly efficient catalysts in the form of micro pellets, as confirmed by catalytic tests and XRD, XPS, TEM, SEM, EDX characterization techniques. Catalytic tests are carried out in hydrogen‐rich mixture which contains (vol. %): 1 CO, 65 H2, 10 H2O, 20 CO2, He – balance; weight hourly space velocity is 29,000 cm3gcat−1h−1. The structured catalyst with highly dispersed nickel and optimal chlorine content provides CO removal to a level of <10 ppm in the temperature interval of 230–300 °C. XRD, TEM, SEM and EDX analysis confirm the presence of Ni nanoparticles and CeOCl species in the catalytic coating. XPS study of samples after reductive pretreatment (simulating CO preferential methanation reaction conditions) in the preparation chamber of the spectrometer reveals the metallic state of Ni and high concentrations of Cl and Ce3+ on the catalyst surface. [ABSTRACT FROM AUTHOR]

The thermal behaviour of Ag2[PtCl4] and Ag2[PtCl6] complex salts in inert and reducing atmospheres has been studied. The thermolysis of compounds in a helium atmosphere is shown to occur in two stages. At the first stage, the complexes decompose in the temperature range of 350–500 °C with the formation of platinum and silver chloride and the release of chlorine gas. At the second stage, silver chloride is sublimated in the temperature range of 700–900 °C, while metallic platinum remains in the solid phase. In contrast to the thermolysis of Ag2[PtCl6], the thermal decomposition of Ag2[PtCl4] at 350 °C is accompanied by significant heat release, which is associated with disproportionation of the initial salt to Ag2[PtCl6], silver chloride, and platinum metal. It is confirmed by DSC measurements, DFT calculations of a suggested reaction, and XRD. The thermolysis of Ag2[PtCl4] and Ag2[PtCl6] compounds is shown to occur in a hydrogen atmosphere in two poorly separable steps. The compounds are decomposed within 170–350 °C, and silver and platinum are reduced to a metallic state, while a metastable single-phase solid solution of Ag0.67Pt0.33 is formed. The catalytic activity of the resulting nanoalloy Ag0.67Pt0.33 is studied in the reaction of CO total (TOX) and preferential (PROX) oxidation. Ag0.67Pt0.33 enhanced Pt nano-powder activity in CO TOX, but was not selective in CO PROX. [ABSTRACT FROM AUTHOR]

Hydrogenation of CO2 relative to valuable chemical compounds such as methanol or dimethyl ether (DME) is an attractive route for reducing CO2 emissions in the atmosphere. In the present work, the hydrogenation of CO2 into DME over CuO-In2O3, supported on halloysite nanotubes (HNT) was investigated in the temperature range 200–300 °C at 40 atm. HNT appears to be novel promising support for bifunctional catalysts due to its thermal stability and the presence of acidic sites on its surface. CuO-In2O3/HNT catalysts demonstrate higher CO2 conversion and DME selectivity compared to non-indium CuO/HNT catalysts. The catalysts were investigated by N2 adsorption, X-ray diffraction, hydrogen-temperature programmed reduction and transition electron microscopy. The acid sites were analyzed by temperature programmed desorption of ammonia. It was shown that CuO/HNT was unstable under reaction conditions in contrast to CuO-In2O3/HNT. The best CuO-In2O3/HNT catalyst provided CO2 conversion of 7.6% with 65% DME selectivity under P = 40 atm, T = 250 °C, gas hour space velocity 12,000 h−1 and H2:CO2 = 3:1. [ABSTRACT FROM AUTHOR]

Highlights: [•] [Pd(NH3)4]MoO4 as a precursor for Pd–Mo-containing catalysts. [•] Different products are formed depending on atmosphere of thermal decomposition. [•] Thermolysis in He atmosphere affords finely mixed two-phase nanosized system Pd–MoO2. [•] Pd–MoO2 system can be a promising catalyst both in pure and supported form. [Copyright &y& Elsevier]