Effect of Cu Addition on the Selectivity of Ni-Based Catalysts for Methylcyclohexane Dehydrogenation

Abstract The storage and distribution of H 2 represent major challenges for its widespread utilization. Liquid organic hydrogen carriers (LOHC), such as methylcyclohexane (MCH), offer a promising alternative by enabling H 2 delivery through dehydrogenation to toluene. Although Pt-based catalysts are the state of the art for this process, this study investigates Ni–Cu catalysts as non-noble metal alternative. For this purpose, two γ -Al 2 O 3 –supported bimetallic Ni-Cu catalysts were prepared at Cu/Ni atomic ratios of 0.25 and 0.56 and their activity and selectivity towards toluene were evaluated and compared with monometallic Pt (0.6 wt%), Ni (12.8 wt%) and Cu (20.0 wt%) γ -Al 2 O 3 –supported catalysts. The experimental evaluation was carried out in a fixed-bed reactor at a temperature and pressure of 320 °C and 1.5 bara respectively, and at a weight hourly space velocity of 2.2 h −1 . Characterization of the synthesized Ni–Cu catalysts indicated the absence of alloy formation under the synthesis conditions. Experimental results indicated that the bimetallic catalysts exhibited increased activity and selectivity to toluene compared to the monometallic counterparts (i.e. Ni, Cu). A positive correlation was observed between copper addition and MCH conversion, with the Ni–Cu catalyst having a Cu/Ni ratio of 0.56 exhibiting a sevenfold increase compared to the monometallic Ni (7% compared to 1%) at the studied conditions. Nevertheless, the performance remained considerably lower than that of Pt-based catalysts, which achieved 33% MCH, under the conditions studied. Moreover, the selectivity towards toluene was observed to increase with time on stream stream, initially reaching 88% for Cu/Ni = 0.56, comparing with 60% and 85% for Ni/ γ -Al 2 O 3 and Pt/ γ -Al 2 O 3 respectively. This results suggests that Cu addition can inhibit the hydrodealkylation of toluene, thereby suppressing the dehydrogenation selectivity of unpromoted Pt catalysts. The enhancement in activity of NiCu catalysts is plausibly attributed to the Ni–Cu interactions at the interface, wehreas the improvement in selectivity is considered to arise from the preferential occupation of the C–C cleavage sites on Ni by Cu. However, catalyst stability was not improved by Cu addition with the deactivation rate being positively correlated with Cu content.