Calorimetric Study of Propane and Ethylbenzene on Active Surface on Carbon-Based Catalysts

The use of carbon materials instead of (mixed) metal oxides in selective oxidation catalysis could emerge to be of basic interest for the catalysis community. Low dimensional carbon allotropes such as multiwalled carbon nanotubes (CNTs) with high structural homogeneity provide the characteristics of model catalysts with well defined active sites as compared with polyvalent transition metal oxides featuring complex electronic and spin structures. The oxydehydrogenation (ODH) reaction over carbon has been discovered in 1979 by Alkhazov et al.[1] From the mechanistic point of view, quinone groups are believed be the active site. These nucleophilic oxygen species can selectively abstract hydrogen atoms and the formed phenol groups are subsequently reoxidized by O2. We choose the ODH of propane and ethylbenzene (EB) as the model reactions. Propane is widely investigated as a substrate in this reaction and mechanistic models for the reaction sequence over metal oxide catalysts are nu-merously suggested. It is equipped with a high C–H bond strength (410.5 kJ mol-1). In contrary to the alkane, the weak C-H bond in benzylic position (357.3 kJ mol-1) makes the molecule highly reactive for ODH

Spin catalysts: A quantum trigger for chemical reactions

Spin catalysis allows restrictions of the spin conservation rule to be overcome, and, moreover, provides a tool for fine control of elementary reactions. Spin-conductive solid catalysts make processes over surfaces strongly correlated and also can trigger the direction of the reaction via external magnetic field application. Activation/deactivation of O2 and non-polar small molecules, homolytic bond cleavage, and coupling of radicals are within the practical scope of spin catalysis

Quantum-chemical investigation of hydrocarbon oxidative dehydrogenation over spin-active carbon catalyst clusters

Graphene-like carbon clusters with oxygen-saturated zigzag and armchair edges were used as models for density-functional theory investigations of the oxidative dehydrogenation (ODH) of hydrocarbon molecules over carbon catalysts. The product of the first elementary step of the reaction, which is either a hydrocarbon radical or a surface ether, is found to be strictly dependent on the spin multiplicity of the catalyst, although energies of the initial state are spin-degenerate. The barriers of the first step of the ODH of light hydrocarbons (methane, ethane, and propane) over zigzag-edge carbon clusters are higher (59–104 kJ/mol) than those for ethylbenzene (18–58 kJ/mol), and the barrier of the second H abstraction is generally rate-limiting (82–106 kJ/mol). The armchair edge is passive toward reaction with hydrocarbons, but it reacts almost without a barrier with hydrocarbon radicals. The barrier of reoxidation by O2 was found to decrease from 161 to 69 kJ/mol with an increasing level of saturation with H atoms

Pentlandite rocks as sustainable and stable efficient electrocatalysts for hydrogen generation

The need for sustainable catalysts for an efficient hydrogen evolution reaction is of significant interest for modern society. Inspired by comparable structural properties of [FeNi]-hydrogenase, here we present the natural ore pentlandite (Fe4.5Ni4.5S8) as a direct ‘rock’ electrode material for hydrogen evolution under acidic conditions with an overpotential of 280 mV at 10 mA cm−2. Furthermore, it reaches a value as low as 190 mV after 96 h of electrolysis due to surface sulfur depletion, which may change the electronic structure of the catalytically active nickel–iron centres. The ‘rock’ material shows an unexpected catalytic activity with comparable overpotential and Tafel slope to some well-developed metallic or nanostructured catalysts. Notably, the ‘rock’ material offers high current densities (≤650 mA cm−2) without any loss in activity for approximately 170 h. The superior hydrogen evolution performance of pentlandites as ‘rock’ electrode labels this ore as a promising electrocatalyst for future hydrogen-based economy