High-performance hybrid oxide catalyst of manganese and cobalt for low-pressure methanol synthesis

Carbon dioxide capture and use as a carbon feedstock presents both environmental and industrial benefits. Here we report the discovery of a hybrid oxide catalyst comprising manganese oxide nanoparticles supported on mesoporous spinel cobalt oxide, which catalyses the conversion of carbon dioxide to methanol at high yields. In addition, carboncarbon bond formation is observed through the production of ethylene. We document the existence of an active interface between cobalt oxide surface layers and manganese oxide nanoparticles by using X-ray absorption spectroscopy and electron energy-loss spectroscopy in the scanning transmission electron microscopy mode. Through control experiments, we find that the catalyst's chemical nature and architecture are the key factors in enabling the enhanced methanol synthesis and ethylene production. To demonstrate the industrial applicability, the catalyst is also run under high conversion regimes, showing its potential as a substitute for current methanol synthesis technologies.open2

In Situ Spectroscopic Investigation into the Active Sites for Crotonaldehyde Hydrogenation at the Pt Nanoparticle-Co3O4 Interface

The hydrogenation of crotonaldehyde by platinum nanoparticles supported on cobalt oxide was used as a reaction to probe the effect of the interface between the two materials on the activity and selectivity of the catalyst. Four potential products can be formed by this reaction: propylene, butyraldehyde, crotyl alcohol, and butanol. When Pt nanoparticles are supported on SiO , an inert support, only propylene and butyraldehyde are formed. However, when Pt is supported on cobalt oxide, the alcohols make up roughly 40% of the total activity, indicating that cobalt oxide plays a pivotal role in the reaction, much like other active supports such as TiO . To elucidate the mechanism of alcohol formation, in situ sum frequency generation vibrational spectroscopy (SFG) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) were utilized to probe the reactant adsorption and intermediate formation and the chemical state of the materials under working catalytic conditions. The SFG data indicate that crotonaldehyde adsorbs on the oxide surface, likely through the aldehyde oxygen as well as on the Pt surface through the alkene group. AP-XPS results show that the surface of the Co O support becomes partially reduced under the reaction conditions and Pt exists in its metallic state. Taking these results together, we propose that the crotonaldehyde adsorbs at reduced oxide surface sites and that this adsorption mode is responsible for the production of alcohol products. A platinum nanoparticle density dependence study was also undertaken to change the abundance of interface sites and study their effect on the reaction. The selectivity between the two alcohol products was altered as a function of the Pt nanoparticle density: higher selectivity toward butanol and lower selectivity toward crotyl alcohol was obtained with increasing density, while propylene and butyraldehyde selectivities were constant with respect to density. On the basis of the data presented, we propose that butanol is preferentially formed at the metal-oxide interface, while crotyl alcohol is formed at oxide surface sites by reaction with spillover hydrogen. 2 2 3

Hydroisomerization of n-hexadecane: Remarkable selectivity of mesoporous silica post-synthetically modified with aluminum

As the impact of acids on catalytically driven chemical transformations is tremendous, fundamental understanding of catalytically relevant factors is essential for the design of more efficient solid acid catalysts. In this work, we employed a post-synthetic doping method to synthesize a highly selective hydroisomerization catalyst and to demonstrate the effect of acid strength and density, catalyst microstructure, and platinum nanoparticle size on the reaction rate and selectivity. Aluminum doped mesoporous silica catalyzed gas-phase n-hexadecane isomerization with remarkably high selectivity to monobranched isomers (∼95%), producing a substantially higher amount of isomers than traditional zeolite catalysts. Mildly acidic sites generated by post-synthetic aluminum grafting were found to be the main reason for its high selectivity. The flexibility of the post-synthetic doping method enabled us to systematically explore the effect of the acid site density on the reaction rate and selectivity, which has been extremely difficult to achieve with zeolite catalysts. We found that a higher density of Brønsted acid sites leads to higher cracking of n-hexadecane presumably due to an increased surface residence time. Furthermore, regardless of pore size and microstructure, hydroisomerization turnover frequency linearly increased as a function of Brønsted acid site density. In addition to strength and density of acid sites, platinum nanoparticle size affected catalytic activity and selectivity. The smallest platinum nanoparticles produced the most effective bifunctional catalyst presumably because of higher percolation into aluminum doped mesoporous silica, generating more 'intimate' metallic and acidic sites. Finally, the aluminum doped silica catalyst was shown to retain its remarkable selectivity towards isomers even at increased reaction conversions

In Situ Microscopy and Spectroscopy Applied to Surfaces at Work

The present review discusses the current state of the art microscopic and spectroscopic characterization techniques available to study surfaces and interfaces under working conditions. Microscopic techniques such as environmental transmission electron microscopy and in situ transmission electron microscopy are first discussed showing their applications in the field of nanomaterials and catalysis. Next sum frequency generation vibrational spectroscopy is discussed, giving probing examples of surface studies in gaseous conditions. Synchrotron based X-ray techniques are also examined with a specific focus on ambient pressure X-ray photoelectron and absorption techniques such as near and extended X-ray absorption fine structure. Each of the techniques is evaluated, whilst the pros and cons are discussed in term of surface sensitivity, spatial resolution and/or time resolution. The second part of the articles is articulated around the future of in situ characterization, giving examples of the probable development of the discussed techniques as well as an introduction of emerging tools such as scanning transmission X-ray microscopy, ptychography, and X-ray photon correlation spectroscopy

In Situ Microscopy and Spectroscopy Applied to Surfaces at Work

The present review discusses the current state of the art microscopic and spectroscopic characterization techniques available to study surfaces and interfaces under working conditions. Microscopic techniques such as environmental transmission electron microscopy and in situ transmission electron microscopy are first discussed showing their applications in the field of nanomaterials and catalysis. Next sum frequency generation vibrational spectroscopy is discussed, giving probing examples of surface studies in gaseous conditions. Synchrotron based X-ray techniques are also examined with a specific focus on ambient pressure X-ray photoelectron and absorption techniques such as near and extended X-ray absorption fine structure. Each of the techniques is evaluated, whilst the pros and cons are discussed in term of surface sensitivity, spatial resolution and/or time resolution. The second part of the articles is articulated around the future of in situ characterization, giving examples of the probable development of the discussed techniques as well as an introduction of emerging tools such as scanning transmission X-ray microscopy, ptychography, and X-ray photon correlation spectroscopy

Oxidation of CH4 over Pd supported on TiO2-doped SiO2: Effect of Ti(IV) loading and influence of SO2

Titania-modified silicas with different weight% of TiO2 were prepared by sol–gel method and used as supports for Pd (1 wt%) catalysts. The obtained materials were tested in the oxidation of methane under lean conditions in absence and in presence of SO2. Test reactions were consecutively performed in order to evaluate the thermal stability and poisoning reversibility. Increasing amounts of TiO2 improved the catalytic activity, with an optimum of the performance for 10 wt% TiO2 loading. Moreover, the titaniacontaining catalysts exhibited a superior tolerance towards SO2 by either adding it to the reactants or feeding it as a pure pretreatment atmosphere at 350 8C. Catalysts were characterized by XPS, XRD, FT-IR and BET measurements. According to the structural and surface analyses, the mixed oxides contained Si–O–Ti linkages which were interpreted as being responsible for the enhanced intrinsic activity of supported PdO with respect to PdO on either pure SiO2 or pure TiO2. Moreover, the preferential interaction of the sulfur molecule with TiO2 and the easy SOx desorption from high surface area silica were the determining factors for the superior SO2 tolerance of the TiO2-doped catalysts.info:eu-repo/semantics/publishe

Activation of Tungsten Oxide for Propane Dehydrogenation and Its High Catalytic Activity and Selectivity

Abstract: Dehydrogenation of propane to propene is one of the important reactions for the production of higher-value chemical intermediates. In the commercial processes, platinum- or chromium oxide-based catalysts have been used for catalytic propane dehydrogenation. Herein, we first report that bulk tungsten oxide can serve as the catalyst for propane dehydrogenation. Tungsten oxide is activated by hydrogen pretreatment and/or co-feeding of hydrogen. Its catalytic activity strongly depends on hydrogen pretreatment time and partial pressure of hydrogen in the feed gas. The activation of tungsten oxide by hydrogen is attributed to reduction of the metal oxide and presence of multivalent oxidation states. Comparison of the catalytic performance of partially reduced WO3−xto other highly active metal oxides shows that WO3−xexhibits superior catalytic activity and selectivity than Cr2O3and Ga2O3. The findings of this work provide the possibility for activation of metal oxides for catalytic reactions and the opportunity for the development of new type of catalytic systems utilizing partially reduced metal oxides. Graphical Abstract: [Figure not available: see fulltext.

Surface Composition Changes of Redox Stabilized Bimetallic CoCu Nanoparticles Supported on Silica under H₂ and O₂ Atmospheres and During Reaction between CO₂ and H₂: In Situ X-ray Spectroscopic Characterization

In this paper, we report the colloidal synthesis and detailed characterization of 11 nm bimetallic CoCu nanoparticle catalysts. Presently Co and Cu is an attractive combination because of their respective properties for industrially important Fischer–Tropsch and methanol synthesis reactions of CO (and CO2) with H2. We report the preparation of catalysts by deposition of bimetallic metal nanoparticles, both within mesoporous silica (MCF-17) and on the native oxide surface of a silicon wafer. Subsequent phase separation into phase-segregated (i.e., dimer) particles is found to occur upon redox treatment. These nanoparticle catalysts have then been investigated using an array of techniques including synchrotron-based ambient pressure X-ray photoelectron spectroscopy (APXPS) and in situ near edge and extended X-ray absorption fine structure (NEXAFS/EXAFS) spectroscopies. CO2 hydrogenation is used as a probe reaction. All three techniques combine to show that an oxygen atmosphere segregates copper to the surface. In doing so the oxygen produces oxides of both Co and Cu metals. Significant hydrogen pressure and temperature are required to fully rereduce both metals to a metallic state as demonstrated by NEXAFS spectroscopy. Under the conditions of the CO2/H2 reaction monitored in situ using NEXAFS spectroscopy, both metals exist in a fully reduced state at 2.7 bar, 1:3 CO2:H2, and 260 °C