Selective hydrogenation and hydrogenolysis of 5‐hydroxymethylfurfural were performed with carbon nanotube‐supported bimetallic NiFe (NiFe/CNT) catalysts. The combination of Ni and Fe in an appropriate atomic ratio of Ni/Fe (2.0) significantly increased the selectivity to 2,5‐furandimethanol or 2,5‐dimethylfuran depending on the reaction temperature. The selectivities to 2,5‐furandimethanol and 2,5‐dimethylfuran were as high as 96.1 % at 383 K and 91.3 % at 473 K, respectively. The characterization results confirmed that bimetallic particles with sizes less than 7 nm were formed on the catalyst. Several key molecules related to 5‐hydroxymethylfurfural transformation were used to investigate the product distribution and reaction pathway. The results indicated that the formation of NiFe alloy species is beneficial to the selective cleavage of the CO bond. Recycling experiments showed that the catalyst can be easily separated with a magnet and reused several times without significant loss of activity.
Toluene methylation with methanol to produce xylene has been widely investigated. A simultaneous side reaction of methanol-to-olefin over zeolites is hard to avoid, resulting in an unsatisfactory methylation efficiency. Here, CO2 and H2 replace methanol in toluene methylation over a class of ZnZrOx–ZSM-5 (ZZO-Z5) dual-functional catalysts. Results demonstrate that the reactive methylation species (H3CO*; * represents a surface species) are generated more easily by CO2 hydrogenation than by methanol dehydrogenation. Catalytic performance tests on a fixed-bed reactor show that 92.4% xylene selectivity in CO-free products and 70.8% para-xylene selectivity in xylene are obtained on each optimized catalyst. Isotope effects of H2/D2 and CO2/13CO2 indicate that xylene product is substantially generated from toluene methylation rather than disproportionation. A mechanism involving generation of reactive methylation species on ZZO by CO2 hydrogenation and migration of the methylation species to Z5 pore for the toluene methylation to form xylene is proposed.
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