Incipient wetness impregnation and a novel deposition symproportionation precipitation were used for the preparation of MnOx/CNT electrocatalysts for efficient water splitting. Nanostructured manganese oxides have been dispersed on commercial carbon nanotubes as a result of both preparation methods. A strong influence of the preparation history on the electrocatalytic performance was observed. The as-prepared state of a 6.5 wt. % MnOx/CNT sample could be comprehensively characterized by comparison to an unsupported MnOx reference sample. Various characterization techniques revealed distinct differences in the oxidation state of the Mn centers in the as-prepared samples as a result of the two different preparation methods. As expected, the oxidation state is higher and near +4 for the symproportionated MnOx compared to the impregnated sample, where +2 was found. In both cases an easy adjustability of the oxidation state of Mn by post-treatment of the catalysts was observed as a function of oxygen partial pressure and temperature. Similar adjustments of the oxidation state are also expected to happen under water splitting conditions. In particular, the 5 wt. % MnO/CNT sample obtained by conventional impregnation was identified as a promising catalytic anode material for water electrolysis at neutral pH showing high activity and stability. Importantly, this catalytic material is comparable to state-of-art MnOx catalyst operating in strongly alkaline solutions and, therefore, offers advantages for hydrogen production from waste and sea water under neutral, hence, environmentally benign conditions

The efficient conversion of CO 2 into various chemicals and fuels is a prospective building block for the more sustainable use of our global resources. [1] Among the various strategies that have been proposed for converting CO 2 into higherenergy intermediates, [2] processes that employ heterogeneous catalysis are of special interest, because they are scalable, based on a mature and flexible technology that has already been applied in the chemical industry, and can be integrated into existing value chains. [3] The dry reforming of methane (DRM) with carbon dioxide is an interesting method for converting these two greenhouse gases into CO/H 2 mixtures [Eq. (1)]. This reaction opens the door to utilizing anthropogenic CO 2 , which is obtained from, for example, oxy-fuel-combustion processes, in the well-established downstream chemistry of syngas to afford MeOH and other base chemicals or fuels through Fischer-Tropsch synthesis.The highly endothermic DRM reaction has long been studied as a potential alternative for the steam reforming of methane and several comprehensive reviews have been published on this topic. [4][5][6] It is well-known that Ru, Rh, and Pt catalysts are very active in this reaction. Active base metals-and Ni in particular-suffer from fast deactivation by coking. [7,8] However, from an economic point of view, Ni-based catalysts are more suitable for commercial applications than noble-metal ones. Thus, a current challenge is to find a noble-metal-free catalyst that is resistant towards coking. [9] Promising approaches in the literature include the poisoning of coke-forming sites by sulfur, [10] variation of the support, [11] in particular through the application of Lewis-basic materials, [12] the addition of alkaline or alkaline-earth oxides as promoters, [13][14] and the incorporation of Ni into a perovskite framework. [15] It has been shown that the deposition of carbon over Ni at 700 8C and over Rh at 750 8C originates from the exothermic Boudouard reaction [Eq. (2)] and not primarily from methane decomposition [Eq. (3)]. [16,17] 2 CO $ CO 2 þC DH 298 ¼ À172 kJ mol À1 ð2ÞThus, the process temperature is an important parameter in the DRM reaction. [4] Considering the thermodynamics of the desired endothermic DRM and of the undesired exothermic Boudouard reaction, a promising way of suppressing coking would be to perform the DRM reaction at high temperatures. [18] Typically, 750 8C is an upper limit in many literature reports. In addition, the thermodynamic yields of CO and H 2 would increase at higher temperatures. Following this concept, the primary challenge in making the Ni particles kinetically more resistant to coking involves making a large Ni surface area thermally stable against sintering at more elevated temperatures. Herein, we report the synthesis, characterization andThe catalytic performance of a Ni/MgAlO x catalyst was investigated in the high temperature CO 2 reforming of CH 4 . The catalyst was developed using a Ni, Mg, Al hydrotalcite-like precursor obtained by co-precipitation. ...

Dry reforming of methane (DRM) has been studied for many years as an attractive option to produce synthesis gas. However, catalyst deactivation by coking over nonprecious-metal catalysts still remains unresolved. Here, we study the influence of structural and compositional properties of nickel catalysts on the catalytic performance and coking propensity in the DRM. A series of bulk catalysts with different Ni contents was synthesized by calcination of hydrotalcite-like precursors Ni_xMg_0.67-xAl_0.33(OH)₂(CO₃)_0.17·mH₂O prepared by constant-pH coprecipitation. The obtained Ni/MgAl oxide catalysts contain Ni nanoparticles with diameters between 7 and 20 nm. High-resolution transmission electron microscopy (HR-TEM) revealed a nickel aluminate overgrowth on the Ni particles, which could be confirmed by Fourier transform infrared (FTIR) spectroscopy. In particular, catalysts with low Ni contents (5 mol %) exhibit predominantly oxidic surfaces dominated by Ni²⁺ and additionally some isolated Ni⁰ sites. These properties, which are determined by the overgrowth, effectively diminish the formation of coke during the DRM, while the activity is preserved. A large (TEM) and dynamic (microcalorimetry) metallic Ni surface at high Ni contents (50 mol %) causes significant coke formation during the DRM

Chlorine evolution is one of the most important electrochemical reactions applied in industry. We present a method for the synthesis of chlorine evolution catalysts with improved performance. The performance increase results from the introduction of controlled mesoporosity into the pore system of Ru- and Ir-containing TiO2 catalysts by pore templating with micelles of amphiphilic block-copolymers. Micelle-templated TiO2-based catalysts were synthesized with loadings up to 15 wt % of either Ru, Ir, or a combination of both active metals. The catalysts’ walls are composed of nanocrystalline mixed oxides with rutile structure. The templated mesopores are about 10 nm in size and form an ordered cubic pore system with good pore connectivity. All studied catalysts are active in chlorine evolution. Adding templated mesoporosity doubles the catalyst performance at identical catalyst composition. The influences of film thickness, composition, and porosity of the developed catalytic coatings on the catalytic performance are discussed.

Dry reforming of methane (DRM) over nickel in a fixed-bed reactor of spheres was studied experimentally and with CFD simulations. Temperature and mole fraction profiles were measured in a dedicated profile reactor as function of axial coordinate. Particle-resolved CFD simulations took into account conjugate heat transfer, surface-to-surface radiation, and surface reactions described by microkinetics. Energy transport of CFD simulations were verified by studying heat transfer without chemical reactions. DRM experiments could not be reproduced with the original microkinetics formulation, even with the axial temperature profile applied. A detailed analysis of the microkinetics showed that thermodynamic inconsistencies are present, which are amplified by high surface coverage of CO*. After modifying the mechanism the experiments could be reproduced. This study shows how complex interactions between local transport phenomena and local kinetics can be quantified without relying on transport correlations