Highly Active and Recyclable Metal Oxide Catalysts for the Prins Condensation of Biorenewable Feedstocks

Feasibility of Ethylene Synthesis via Oxidative Coupling of Methane

Electrochemical Synthesis of H2O2 by Two-Electron Water Oxidation Reaction

A newly designed downdraft wood stove achieved low-emission heating by integrating an alumina-supported mixed metal oxide catalyst in the combustion chamber operated under high temperature conditions. In the first step, a catalyst screening has been carried out with a lab-scale plug flow reactor in order to identify the potentially active mixed metal oxide catalysts. Mixed metal oxide catalysts have been the center of attention because of their expected high temperature stability and activity. The catalyst has been synthesized through two novel routes, and it has been integrated into a downdraft wood stove. The alumina-supported mixed metal oxide catalyst reduced the volatile hydrocarbons, carbon monoxide and carbonaceous aerosols by more than 60%.

Different knitted silica-fibre supported metal oxides (oxides of Co, Ni, Mn, Cr) and various combinations of them, platinum-activated cobalt and nickel oxide catalysts as well as noble metal (Pt, Pd) catalysts were prepared. The catalysts were tested for their activity in propane and natural gas combustion in a continuous flow tube reactor at temperature range of 423-823 K and GHSV of 23900 and 47800 h−1. High combustion efficiencies were obtained by the metal oxides and platinum activated metal oxides. Co3O4 was found to be the most active single metal oxide catalyst in propane combustion. The low temperature activity of metal oxide was strongly improved by use of platinum as an activator. The propane combustion over Pd/SiO2 was found to be structure sensitive under our experimental conditions. The dependence of the rate of propane combustion over noble metal containing catalysts was found to be zero order with respect to oxygen and one with respect to propane. The reaction orders over metal oxides were fractional (0 < n,m < 1). The catalysis were more active in propane than in natural gas combustion. NiO and Pd were found to be the most active catalysts in natural gas combustion. The activity pattern of the prepared catalysts in complete oxidation of propane and natural gas is reported. The catalysts were characterized by O2-TPD and the chemisorption of propane, carbon monoxide and hydrogen.

Iron-manganese mixed metal oxide catalysts with a range of Fe:Mn ratios were synthesised by co-precipitation using sodium carbonate and evaluated for total propane oxidation. The Fe0.50Mn0.50Ox catalyst was the most active, and this was due to increased surface area along with the formation of a Mn2O3 phase that was not present in the other catalysts. The effect of the precipitating agent was evaluated with the Fe0.50Mn0.50Ox catalyst, investigating preparation using (NH4)2CO3, K2CO3, NH4OH, KOH, and NaOH. In almost all cases, the activity of propane oxidation was increased compared to the Na2CO3-prepared catalyst, with the hydroxide-precipitated catalysts generally being more active than the carbonates. The NH4OH catalyst was the best performing and this was thought to be due to the formation of a highly active mixed defect spinel structure. Results demonstrate that highly active mixed metal oxide total oxidation catalysts can be prepared using abundant elements, and the choice of precipitating agent is important to maximise the activity.

Selective alcohol oxidation to aldehydes and ketones over base-promoted gold–palladium clusters as recyclable quasihomogeneous and heterogeneous metal catalysts

The Pechini method allows for compositional and structural control of mixed ruthenium–iridium powder samples. Extensive characterization reveals that the calcination step leads to agglomerates with a metallic core that is encapsulated by the mixed RuxIr1–xO2 oxides. In the composition range of 21 up to 74 mol % ruthenium, the metal core reveals a miscibility gap with an Ir-rich fcc structure and a Ru-enriched hcp structure. Quite in contrast, the mixed oxide particles form a well-defined RuxIr1–xO2 solid solution throughout the entire composition range. Catalytic activity tests of the mixed RuxIr1–xO2 oxide catalysts are conducted with the prototypical CO oxidation reaction under oxidizing and under both stoichiometric reaction conditions; note that the metallic core is buried and does therefore not contribute to the activity. The least active catalyst is pure IrO2. At moderate reaction temperatures above 100 °C, the most active oxidation catalyst is identified with the Ir0.125Ru0.875O2 mixed oxide. All mixed RuxIr1–xO2 oxide catalysts are bulk-stable under the reaction conditions considered. However, upon CO oxidation reaction, the Ir4+ concentration at the mixed oxide surface is significantly enhanced with respect to its bulk composition. This information may be important for other catalytic oxidation reactions as well, such as the anodic oxygen evolution reaction in the electrocatalytic water splitting.

Hot-gas desulfurization is an important step for optimizing the process economics of new schemes for power generation from coal. Mixed oxides such as CuO•Al[2]O[3] and Fe[2]O[3]•Al[2]O[3] are attractive as high-temperature, regenerable, desulfurization sorbents because they exhibit higher performance than CuO and Fe[2]O[3]. Mixed copper-aluminum and iron-aluminum oxides were prepared in porous form by the citrate process under various calcination conditions for subsequent reduction and sulfidation studies. The oxide samples were characterized by several techniques to determine chemical structure and texture. For the mixed copper-aluminum oxides, atomic absorption spectroscopy (AAS) provided the fractions of copper, soluble and insoluble, in hot nitric acid which closely corresponded to CuO and CuAl[2]O[4], respectively; x-ray diffraction (XRD) provided complementary information about the content of the pure and compound oxides; and a combination of x-ray line broadening, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) provided an estimate of the size of crystallites or phase domains. For the mixed iron-aluminum oxides, XRD identified crystalline phases, SEM revealed the changing surface texture with iron composition, and BET surface area measurements indicated the content of free alumina. Temperature-programmed reduction (TPR) of mixed oxides was more complex than TPR of the pure, reducible oxides. The compound oxide, CuAl[2]O[4], and part of CuO closely associated with Al[2]O[3] were reduced much more slowly than bulk CuO. Similarly, the compound oxide, FeAl[2]O[4], a solid solution between Fe[3]O[4] and FeAl[2]O[4], and Fe[3]O[4] in close association with alumina were reduced much more slowly than bulk Fe[3]O[4]. While oxides of +1 oxidation state, Cu[2]O and CuAlO[2], were identified as reduction intermediates for TPR of CuAl[2]O[4], no oxides of +1 oxidation state were identified for reduction of iron-aluminum oxides. Mixed copper-aluminum oxides were studied more extensively than mixed iron-aluminum oxides. The interaction between CuO and Al[2]O[3] seen in TPR studies was further examined by XRD, diffuse reflectance spectroscopy, and laser Raman spectroscopy. Pronounced sintering of CuAl[2]O[4] was observed to commence at temperatures in excess of 700°C, and the dispersion of copper on reduction of CuAl[2]O[4] was poorer than that obtained by reduction of mixed oxide, CuO and Al[2]O[3]. In studies using a thermogravimetric analyzer, sulfidation of reduced sorbents produced high-temperature digenite (Cu[9+x]S[5]) in the case of copper aluminum samples, and high-temperature pyrrhotite (Fe[1]-[x]S) in the case of iron-aluminum samples as the major crystalline products. Both CuAl[2]O[4] and FeAl[2]O[4] were found to be resistant to sulfidation as compared to the pure oxides, CuO and Fe[2]O[3], and to mixed oxides, CuO-Al[2]O[3] and Fe[2]O[3]-Al[2]O[3]. Formation of copper sulfate during air regeneration of sulfided Cu-Al-O samples was increased in the presence of free alumina

The development of efficient, abundant, and inexpensive oxygen reaction catalysts is essential for renewable energy research. The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) play critical roles in the development of important energy conversion and storage devices - fuel cells and metal-air batteries - and in the generation of hydrogen as a renewable fuel via water splitting [1,2]. While significant advances in both the mechanistic understanding of these reactions and catalyst design have been achieved in recent years [3], materials based on expensive rare earth metals such as platinum, iridium and ruthenium are still the most commonly used commercial catalysts [4]. Optimizing the oxygen reactions using low cost materials is therefore the key to maximising the commercial potential of these devices. In this respect, the oxides of non-precious metals such as nickel and iron, are attractive catalyst candidates [5-7]. Their high abundance and low cost make them economically viable alternatives to state-of-the-art noble metal catalysts, and the formation of a range of mixed metal oxides provides practical routes for catalytic enhancement. In particular, the beneficial effect of Fe impurities on the OER activity of Ni hydroxides was reported over 25 years ago [8] and since then Ni-Fe based oxide catalysts have been shown to be some of the most active OER catalysts in alkaline media [5-7,9]. However, this synergistic relationship has yet to be fully explored for the ORR. Although several Ni-Fe based ORR catalysts have been developed [10-12], these materials typically contain Pt as the active component with Ni and Fe acting simply to reduce the Pt loading rather than as the active catalysts. In this work, we focus on the development and electrocatalytic activity of a range of Pt free Ni-Fe based mixed oxide catalysts for the ORR. The catalyst layers are prepared electrochemically using a simple and scalable potential cycling methodology on macro-scale substrates and chip-scale microelectrode arrays. The effect of substrate and oxide composition on the stability and electrocatalytic performance of the mixed oxides is highlighted and the mixed oxides are shown to exhibit high stability and reusability under catalytic conditions. The electrocatalytic properties of the catalyst layers are examined using a combination of hydrodynamic voltammetry and electrochemical impedance spectroscopy allowing the determination of kinetically significant parameters including Tafel slopes, electrochemical rate constants and reaction orders. Finally, these experimentally determined kinetic parameters have been combined with COMSOL simulations to provide a detailed understanding of the kinetics of oxygen reduction at Ni-Fe oxides. 1. L. Zhou, Renewable Sustainable Energy Review, 9, 395 (2005) 2. R. Schlogl, ChemSusChem, 3, 209 (2010) 3. H. Dau, C. Limberg, T. Reier, M. Risch, S. Roggan, P. Strasser, Chem. Cat. Chem., 2, 724 (2010) 4. K. Kinoshita, Electrochemical Oxygen Technology, (Wiley, New York, 1992). 5. M. D. Merrill, R. C. Dougherty, J. Phys. Chem. C, 112, 3655 (2008) 6. C. C. L. McCrory, S. H. Jung, J. C. Peters, T. F. Jaramillo, J. Am. Chem. Soc., 135, 16977 (2013) 7. M. W. Louie, A. T. Bell, J. Am. Chem. Soc., 135, 12329 (2013) 8. J. Desilvestro, D.A. Corrigan, M.J. Weaver, J. Phys. Chem., 90, 6408 (1986) 9. L. Trotochaud, J.K. Ranney, K.N. Williams, S.W. Boettcher, J. Am. Chem. Soc., 134, 17253 (2012) 10. H. Zhu, S. Zhang, S. Guo, D. Su, S. Sun, J. Am. Chem. Soc., 135, 7130 (2013) 11. Y. Li, F. Quan, L. Chen, W. Zhang, H. Yu, C. Chen, RSC Adv., 4, 1895 (2014) 12. B. Li, S. H. Chan, Int. J. Hydrogen Energy, 38, 3338 (2013)

The heterogeneous metathesis of light olefins is a crucial reaction for the regulation of olefins stocks at low energy cost. Molybdenum oxide dispersed at the surface of an inorganic support is a regarded cheap and robust heterogeneous metathesis catalyst. This thesis presents fundamental and applied approaches to the understanding of the active species and to the development of new efficient catalytic materials. A systematic investigation of MoO3/SiO2-(Al2O3) catalysts with variable support composition describes the crucial role of Al. Then, the best support composition is selected and a classical wet impregnation preparation method is inspected in details. For these catalysts, the genesis of active and inactive species during the preparation is described in link with the (limited) performances reached. Alternative MoO3 deposition modes are then explored. Firstly, the wet impregnation with alternative Mo precursors (use of oxalic acid additive or use of molybdenum oxide hydrates solutions) allows impeding the formation of inactive Mo species upon calcination and produces more active catalysts. Secondly, the direct thermal spreading of MoO3 onto the support is identified as an alternative straightforward route to obtain active metathesis catalysts. An innovative non-hydrolytic sol-gel method is then implemented to prepare MoO3-SiO2-Al2O3 mixed oxides. Upon optimization of homogeneity, texture and composition, these samples turn out to be very active metathesis catalysts because highly dispersed molybdate species are stabilized at their surface.

The design and synthesis of highly active non-noble metal oxide catalysts, such as transition- and rare-earth-metal oxides, have attracted significant attention because of their high efficiency and low cost and the resultant potential applications for the degradation of volatile organic compounds (VOCs). The structure-activity relationships have been well-studied and used to facilitate design of the structure and composition of highly active catalysts. Recently, non-noble metal oxides with porous structures have been used as catalysts for deep oxidation of VOCs, such as aromatic hydrocarbons, aliphatic compounds, aldehydes, and alcohols, with comparable activities to their noble metal counterparts. This review summarizes the growing literature regarding the use of porous metal oxides for the catalytic removal of VOCs, with emphasis on design of the composition and structure and typical synthetic technologies.

Influence of the preparation method on the structural properties of mixed metal oxides

The conversion of methane to a value-added chemical is important for methane utilization and industrial demand for primary chemicals. Oxidative coupling of methane (OCM) to C2 hydrocarbons is one of the most attractive ways to use natural gas. However, it is difficult to obtain higher C2 yield in classic OCM reaction due to a favorable COx formation. Regarding this, various catalysts for OCM have been studied to fulfill desirable C2 yields. In this review, we briefly overview the single metal oxide types of OCM catalysts (alkaline-earth metal oxides and rare-earth metal oxides) and highlight the characteristics of catalysts in OCM reaction such as methane activation, surface basicity and lattice oxygen.

Metal oxide-catalyzed hydrothermal liquefaction of Malaysian oil palm biomass to bio-oil under supercritical condition

High-temperature thermochemical energy storage based on redox reactions using Co-Fe and Mn-Fe mixed metal oxides