The use of gallium-rich, Supported Catalytically Active Liquid Metal Solution (SCALMS) is a promising new concept to achieve catalysis with atomically dispersed active metal atoms. Expanding our previous work on short alkane dehydrogenation, we present here the application of SCALMS for the dehydrogenation of methylcyclohexane (MCH) to toluene (TOL) using a Ga 52 Pt alloy (liquid under reaction conditions) supported on silica. Cycloalkane dehydrogenation catalysis has attracted great attention recently in the context of hydrogen storage concepts using liquid organic hydrogen carrier (LOHC) systems. The system under investigation showed high activity and stable conversion of MCH at 450°C and atmospheric pressure for more than 75 h time-on-stream (X MCH = 15 %) with stable toluene selectivity (S TOL) of 85 %. Compared to commercially available Pt/SiO 2 , the SCALMS system resulted in higher yields and robustness. Baseline experiments with Pt-free Ga/SiO 2 under identical conditions revealed the decisive influence of Pt dissolved in the liquid Ga matrix.
The preparation of supported catalytically active metal solutions has been investigated using ultrasonication. Sonication conditions and solvents influence the Ga droplet formation and hence the catalytic performance in heptane dehydrogenation.
In this work, we demonstrate RuP 2 -MoP catalysts being highly stable and selective for the dehydrogenation of long-chain alkanes like n-heptane. Compared to a monometallic MoP catalyst, the bimetallic system substantially increases n-heptene selectivity from 40 % towards 80 %. This effect can be traced back to a reduced surface acidity, suppressing the competitive hydrogenolysis reaction. The active transition metal phosphide is, furthermore, compared to its phosphorous-free RuMocounterpart. As revealed by STEM-EDX investigations, incorporation of phosphorous results in the formation of separated metal phosphide clusters instead of an intermetallic alloy. In the dehydrogenation of n-heptane the phosphorous modification clearly avoids catalyst deactivation and maintains the high nheptene selectivity. X-ray diffraction, elemental analysis and STEM-EDX further reveal that catalyst coking and the formation of less active molybdenum carbide phases is effectively suppressed by phosphorous incorporation, making RuP 2 -MoP an attractive system for selective dehydrogenation of long-chain alkanes.
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