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To compare the inherent methanol steam reforming properties of intermetallic compounds and a corresponding intermetallic compound-oxide interface, we selected the Cu-In system as a model to correlate the stability limits, self-activation and redox activation properties with the catalytic performance. Three distinct intermetallic Cu-In compounds - Cu7In3, Cu2In and Cu11In9 - were studied both in an untreated and redox-activated state resulting from alternating oxidation-reduction cycles. The stability of all studied intermetallic compounds during methanol steam reforming (MSR) operation is essentially independent of the initial stoichiometry and all accordingly resist substantial structural changes. The inherent activity under batch MSR conditions is highest for Cu2In, corroborating the results of a Cu2In/In2O3 sample accessed through reactive metal-support interaction. Under flow MSR operation, Cu7In3 displays considerable deactivation, while Cu2In and Cu11In9 feature stable performance at simultaneously high CO2 selectivity. The missing significant self-activation is most evident in the operando thermogravimetric experiments, where no oxidation is detected for any of the intermetallic compounds. In situ X-ray diffraction allowed us to monitor the partial decomposition and redox activation of the Cu-In intermetallic compounds into Cu0.9In0.1/In2O3 (from Cu7In3), Cu7In3/In2O3 (from Cu2In) and Cu7In3/Cu0.9In0.1/In2O3 (from Cu11In9) interfaces with superior MSR performance compared to the untreated samples. Although the catalytic profiles appear surprisingly similar, the latter interface with the highest indium content exhibits the least deactivation, which we explain by formation of stabilizing In2O3 patches under MSR conditions.

We assessed the catalytic properties of the Cu/ZrO2 interface in methanol and formaldehyde steam reforming (MSR and FSR) on powder catalysts by using a comparative approach with respect to the influence of the ZrO2 polymorph support structure (monoclinic (m-)ZrO2 vs. tetragonal (t-)ZrO2), its synthesis routine and the choice of the precursor material on the CO2 selectivity. Our studies reveal that ZrO2 exhibits a pronounced versatility as a support material and its catalytic properties depend most strongly on its surface properties governed by its synthesis, especially by the choice of the Zr precursor. The way of combining the support with copper introduces an additional layer of complexity, but its influence on the MSR performance is limited to a modification of the conditions provided by the ZrO2 support. Exploiting the comparative approach regarding the Cu-ZrO2 catalysts in FSR and MSR – including the pure support materials – in combination with in situ Fourier transform infrared (FT-IR) spectroscopy shows that the CO observed in MSR on Cu/m-ZrO2 can be attributed to a spillover of formaldehyde to the support. Side reactions of m-ZrO2 are suppressed at lower temperatures due to its lack of highly reactive sites, resulting in a CO2-selective MSR performance. In Cu/t-ZrO2, however, the amount of CO is higher and a combination of a formaldehyde spillover to the support and a Cu-ZrO2 phase boundary yielding CO leads to the lower CO2 selectivity of these samples. An elevated number of defects and reactive Lewis acidic and Bronsted basic centers of t-ZrO2 explains this increased activity towards side reactions in contrast to Cu/m-ZrO2 catalysts.

A series of novel melilite-type structured compounds of the general formula Sr2Mg1−xMnxGe2−ySiyO7+δ (0 ≤ x ≤ 1; 0 ≤ y ≤ 2) was produced by conventional solid-state syntheses and subsequently characterized by X-ray powder diffraction (XRPD) and Rietveld analysis. All prepared compounds crystallize in the tetragonal space group P21m with the unit cell dimensions varying dependent on the elements contained in the structure. The diffuse reflectance spectra of the obtained powders were recorded, and the color properties were determined by means of the CIE 1976 L*a*b* color coordinates. With the aim of developing new, non-toxic inorganic blue materials that might be of interest for industrial applications, the expensive element Ge was substituted with Si, while the Mg to Mn ratio was simultaneously varied for color optimization. XPS measurements provided evidence that the blue color displayed by some of the candidates in the melilite-type structure is attributable to the presence of the manganese in a mixed oxidation state of 2+/3+. Finally, the highest blue color value was achieved for Sr2Mg0.2Mn0.8Si2O7+δ with b* = −31.3, a remarkable value for an environmentally safe inorganic blue pigment.

To evaluate the structural and spectroscopic steering factors of noble metal promotion in the catalytic reduction of NO by CO, a series of La(Cu0.7Mn0.3)0.98M0.02O3−δ (M = Pd, Pt, Ru, Rh) perovskite catalysts is investigated. The materials are synthesized by a sol-gel method and characterized by X-ray powder diffraction (XRD), electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). All metal-promoted perovskites exhibit a comparatively higher activity for catalytic reduction of NO by CO with respect to pure La(Cu0.7Mn0.3)O3−δ . Among all catalysts tested, the La(Cu0.7Mn0.3)0.98Pd0.02O3−δ perovskite shows the highest catalytic activity, which is tentatively related to a combined synergistic effect of improved oxygen vacancy activity and noble metals. Additionally, the redox chemistry of the catalysts in different reducing (H2) and oxidizing (NO, O2) atmospheres is tested. An enhanced kinetic reducibility, especially with Pd, was observed. All the H2-reduced catalysts are capable of reducing NO. At low and intermediate temperatures, the formation of N2O is observed, but at higher temperatures NO is exclusively converted to N2. The introduction of noble metals leads to new adsorption sites for NO. As XPS suggests a tendency for depletion of noble metals in the surface-near regions, while the catalytic activity in NO reduction at the same time appears much improved, directed noble metal promotion with modest amounts especially in surface-near regions during synthesis appears as an encouraging method to economize the use of the latter. This work was performed within the framework of the funding programme IMPULSE Iran Austria, financed by funds of the OeAD fonds and of the Ministry of Science, Research and Technology of the Islamic Republic of Iran. We also thank the SFB F45-N16 special research program for financial support. This work was performed within the framework of the research platform ‘‘Materials and Nanoscience” and the special PhD program ‘‘Reactivity and Catalysis”, both at the University of Innsbruck.

The reactive metal-support interaction in the Cu-In2O3 system and its implications on the CO2 selectivity in methanol steam reforming (MSR) have been assessed using nanosized Cu particles on a powdered cubic In2O3 support. Reduction in hydrogen at 300 °C resulted in the formation of metallic Cu particles on In2O3. This system already represents a highly CO2-selective MSR catalyst with ~93% selectivity, but only 56% methanol conversion and a maximum H2 formation rate of 1.3 µmol gCu−1 s−1. After reduction at 400 °C, the system enters an In2O3-supported intermetallic compound state with Cu2In as the majority phase. Cu2In exhibits markedly different self-activating properties at equally pronounced CO2 selectivities between 92% and 94%. A methanol conversion improvement from roughly 64% to 84% accompanied by an increase in the maximum hydrogen formation rate from 1.8 to 3.8 µmol gCu−1 s−1 has been observed from the first to the fourth consecutive runs. The presented results directly show the prospective properties of a new class of Cu-based intermetallic materials, beneficially combining the MSR properties of the catalyst’s constituents Cu and In2O3. In essence, the results also open up the pathway to in-depth development of potentially CO2-selective bulk intermetallic Cu-In compounds with well-defined stoichiometry in MSR., Graphical abstract

We describe a new type of operando Fourier transform infrared (FTIR)–mass spectrometry setup for surface-chemical and reactivity characterization of heterogeneous catalysts. On the basis of a sophisticated all-quartz FTIR reactor cell, capable of operating between room temperature and 1000 °C in reactive gas atmospheres, the setup offers a unique opportunity to simultaneously collect and accordingly correlate FTIR surface-chemical adsorption data of the active catalyst state and FTIR gas phase data with complementary reactivity data obtained via mass spectrometry in situ. The full set of catalytic operation modes (recirculating static and flow reactor conditions) is accessible and can be complemented with a variety of temperature-programmed reaction modes or thermal desorption. Due to the unique transfer process involving a home-built portable glovebox to avoid air exposure, a variety of complementary quasi in situ characterization methods for the pre- and post-reaction catalyst states become accessible. We exemplify the capabilities for additional x-ray photoelectron spectroscopy characterization of surface-chemical states, highlighting the unique strength of combining adsorption, electronic structure, and reactivity data to gain detailed insight into the reactive state of a Cu/ZrO2 heterogeneous catalyst during methanol steam reforming operation.

Structural and chemical consequences of reactive metal-support interaction (RMSI) effects occurring under hydrogen reduction in a metastable metal-oxide system have been exemplified for small PdO particles loaded onto rhombohedral In2O3 (PdO/rh-In2O3) using synchrotron-based in situ X-ray diffraction experiments at temperatures up to 500 °C. rh-In2O3 is a meta-stable In2O3 polymorph that is prone to gas-phase dependent phase transformation to cubic In2O3 (c-In2O3). Cross-influence of metal-support interaction and phase transformation can therefore be expected in similar temperature regimes. To separate both effects, comparable experiments have also been conducted on pure rh-In2O3. Phase transformation of pure rh-In2O3 to cubic In2O3 in hydrogen occurs between 415 °C and 450 °C. On Pd/rh-In2O3, a sequence of PdO reduction to Pd metal, followed by PdH0.706 hydride formation and subsequently, InPd and In3Pd2 intermetallic compound formation have been observed between 30 °C and 500 °C. After the intermetallic compound formation is finished at around 400 °C, the phase transformation to c-In2O3 sets in at exactly the same temperature as on pure rh-In2O3 and extends over the same temperature range. This proves that the phase transformation of rh-In2O3 to c-In2O3 is not influenced by the reduction and the intermetallic compound formation. In contrast to Pd on c-In2O3, In-Pd compound formation from rh-In2O3 occurs at much lower temperatures (230 °C vs. 300 °C), despite finally approaching the same compound stoichiometries (InPd and In3Pd2). This points to a high structural stability of reduced rh-In2O3/stability of oxygen vacancies (compared to c-In2O3) as well as to facilitated diffusion of reduced In(-O) species at low temperatures.

To focus on the influence of the intermetallic compound—oxide interface of Pd-based intermetallic phases in methanol steam reforming (MSR), a co-precipitation pathway has been followed to prepare and subsequently structurally and catalytically characterize a set of nanoparticulate Ga2O3- and In2O3-supported GaPd2 and InPd catalysts, respectively. To study the possible promoting effect of In2O3, an In2O3-doped Ga2O3-supported GaPd2 catalyst has also been examined. While, upon reduction, the same intermetallic compounds are formed, the structure of especially the Ga2O3 support is strikingly different: rhombohedral and spinel-like Ga2O3 phases, as well as hexagonal GaInO3 and rhombohedral In2O3 phases are observed locally on the materials prior to methanol steam reforming by high-resolution transmission electron microscopy. Overall, the structure, phase composition and morphology of the co-precipitated catalysts are much more complex as compared to the respective impregnated counterparts. However, this induces a beneficial effect in activity and CO2 selectivity in MSR. Both Ga2O3 and In2O3 catalysts show a much higher activity, and in the case of GaPd2–Ga2O3, a much higher CO2 selectivity. The promoting effect of In2O3 is also directly detectable, as the CO2 selectivity of the co-precipitated supported Ga2O3–In2O3 catalyst is much higher and comparable to the purely In2O3-supported material, despite the more complex structure and morphology. In all studied cases, no deactivation effects have been observed even after prolonged time-on-stream for 12 h, confirming the stability of the systems.

The catalytic performance of Ag- and Co3O4-impregnated strontium titanium ferrite (SrTi0.7Fe0.3O3-δ, STF) has been assessed in methanol steam reforming as a test reaction and accordingly correlated with spectroscopic and structural characterization after each step of a catalytic cycle including pre-oxidation and pre-reduction. After pre-reduction in hydrogen at 400 °C, metallic silver and oxidized Co in the form of Co3O4 are present. As for catalysis, it was observed that both Ag and Co3O4 are strongly promoting the methanol chemistry with respect to pure STF already at low temperatures (230 °C for both materials). As a consequence, the selectivity towards carbon monoxide is strongly enhanced in comparison to pure STF. On Co3O4-STF, the catalytic profile is basically dominated by a temperature-dependent complex interplay between methanol steam reforming, methanol dehydrogenation and the water-gas shift equilibrium. The results also prove that despite the obvious inadequacy of H2-prereduced Ag-STF to act a...

Starting from subsurface Zr0-doped “inverse” Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state.