In this study, we show the first hydrogen evolution performed in a large‐scale photoreactor under natural sunlight irradiation with a mesoporous carbon nitride photocatalyst immobilized on nine stainless steel plates by drop‐coating. Stable films were obtained producing approximately 18 L gaseous hydrogen within one month time on stream at an average hydrogen evolution reaction (HER) rate of 0.22 L kWh−1. The rate could be nicely predicted from preliminary lab‐scale experiments under well‐defined conditions. Furthermore, the hydrogen production correlates with the sunlight intensity. Based on the total energy input, a maximum solar‐to‐hydrogen (STH) conversion of 0.12 % was obtained.
The oxidative coupling of methane (OCM) is one of the best methods for the direct conversion of methane. Among the known OCM catalysts, Mn x O y-Na 2 WO 4 /SiO 2 is a promising candidate for an industrial application, showing a high methane conversion and C 2 selectivity, with a good stability during long-term catalytic activity tests. In the present study, some results have been already published and discussed briefly in our previous short communication [Yildiz 2014]. However, we herein investigated comprehensively the influence of various silica support materials on the performance of the Mn x O y-Na 2 WO 4 /SiO 2 system in the OCM by means of ex situ and in situ XRD, BET, SEM and TEM characterization methods and showed new results to reveal possible support effects on the catalyst. The catalytic performance of most Mn x O y-Na 2 WO 4 /SiO 2 catalysts supported by different silica support materials did not differ substantially. However, the performance of the SBA-15 supported catalyst was outstanding and the methane conversion was nearly twofold higher in comparison to the other silica supported catalysts at similar C 2 selectivity as shown before in the communication [Yildiz 2014]. The reason of this substantial increase in performance could be the ordered mesoporous structure of the SBA-15 support material, homogeneous dispersion of active components and high number of active sites responsible for the OCM.
The oxidative coupling of methane is a highly promising reaction for its direct conversion. Silica supported Mn(x)O(y)-Na2WO4 is a suitable catalyst for this reaction. In this study, a variety of different SiO2 materials have been tested as supports. Surprisingly, the application of ordered mesoporous silicas, here exemplarily shown for SBA-15 as support materials, greatly enhances the catalytic performance. The CH4 conversion increased two fold and also the C2 selectivity is strongly increased.
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