Electrocatalytic activity of Ni-doped nanoporous carbons in the electrooxidation of propargyl alcohol

Herein, we explore the immobilization of nickel on various carbon supports and their application as electrocatalysts for the oxidation of propargyl alcohol in alkaline medium. In comparison with massive and nanoparticulated nickel electrode systems, Ni-doped nanoporous carbons provided similar propargyl alcohol conversions for very low metallic contents. Nanoparticulated Ni on various carbon supports gave rise to the highest electrocatalytic activity in terms of product selectivity, with a clear dependence on Ni content. The results point to the importance of controlling the dispersion of the Ni phase within the carbon matrix for a full exploitation of the electroactive area of the metal. Additionally, a change in the mechanism of the propargyl alcohol electrooxidation was noted, which seems to be related to the physicochemical properties of the carbon support as well. Thus, the stereoselectivity of the electrooxidative reaction can be controlled by the active nickel content immobilized on the anode, with a preferential oxidation to (Z)-3-(2-propynoxy)-2-propenoic acid with high Ni-loading, and to propiolic acid with low loading of active Ni sites. Moreover, the formation of (E)-3-(2-propynoxy)-2-propenoic acid was discriminatory irrespective of the experimental conditions and Ni loadings on the carbon matrixes.

Methoxylation of α-pinene over mesoporous carbons and microporous carbons: A comparative study

A biomass derived carbon, a commercial microporous carbon and a xerogel mesoporous carbon catalysts were used in the study of α-pinene methoxilation reaction and the influence of textural and physical–chemical properties of the carbons was evaluated. Biomass carbon presented the higher activity, whereas the commercial one is the less active in the conditions studied. The main product of the reaction was α-terpinyl methyl ether and good values of selectivity were obtained over all the catalysts. A kinetic model was developed assuming that the α-pinene is consumed according to the parallel reaction network. The kinetic model presents high quality fittings to the experimental concentration profiles. These results show that it is possible to activate a waste residue using H3PO4 and convert it to high added value product such as acid catalyst.

Structured carbons as supports for hydrogenation hybrid catalysts prepared by the immobilization of a Rh diamine complex

A CNF-monolith sample (carbon nanofibres grown on a ceramic monolith), and a granular carbon xerogel have been used as supports for hybrid catalysts where the active species is an Rh diamine complex. The advantages of these supports are their open porous structure and their morphology, which make catalyst handling easier and avoid difficult separation processes. The obtained catalysts are noticeably more active than the homogeneous Rh complex and are stable against leaching. At first use, partial reduction of the Rh complex takes place and nanometer-sized Rh particles develop, which increases the catalyst activity. Despite the open porous structure, mass transport limitations are present, especially in the case of the carbon xerogel based catalyst. Differences in internal mass transfer limitations are essentially due to the different diffusional path lengths.