ABSTRACT Water-assisted proton hopping (WAPH) plays an important role in the aqueous-phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). In this study, based on a strategy of spontaneously polarized ceramic (SPCE)-reinforced WAPH, a Ni–Co/SPCE–C catalyst was constructed by high-temperature calcination of a dual mechanical activation-treated precursor. Ni–Co/SPCE–C with favorable structural characteristics, intimate interfacial compatibility, and unique spontaneous polarization effect enhanced the migration efficiency of active hydrogen and activated water to form small water clusters, contributing to outstanding catalytic activity for aqueous-phase hydrogenation of LA to produce GVL at relatively low reaction temperature and H 2 pressure. A LA conversion of 99.9% and a GVL yield of 92.3% were achieved at 160°C and 1.5 MPa H 2 over the Ni–Co/SPCE–C catalyst, which were significantly higher than those catalyzed by contrastive catalysts. A variety of tests and theoretical calculations reveal that SPCE with far-infrared emission and surface electric field was conducive to the reduction in the hydrogen spillover energy barrier, the stabilization of the transition state, and the facile exchange of H 2 and water for accelerating WAPH. Moreover, a reasonable SPCE-reinforced WAPH mechanism was proposed to explain the enhanced aqueous hydrogenation of LA. This research can provide valuable insights into the design and development of high-performance non-noble metal catalysts for aqueous hydrogenation applications.
Ni3Co1/ELAC catalyst, prepared by the enzymatically hydrolyzed lignin activated carbon as a carrier and a 3 : 1 ratio content of nickel and cobalt, can selectively convert furfural to cyclopentanol (CPL) in aqueous solution. We used activated carbon prepared by the phosphoric acid method as the carrier, and investigated the effect of the carrier on the catalyst activity. The ratio of bimetal (Ni, Co) content and reaction conditions (reaction temperature, reaction time, initial H2 pressure) have also been investigated in the furfural hydrogenation. With the optimal Ni3Co1/ELAC catalyst, the conversion rate of furfural and the selectivity of CPL were 100% and 94.1%, respectively. In this process, some important catalysts were studied by XRD, XPS, ICP-AES, BET and TEM characterization. Through experimental results and other people's research, we deduced a reasonable reaction path and verified it by replacing the reaction substrate and solvents. Finally, the experiment proved that the formation of CPL by furfural required the occurrence of a rearrangement reaction and the participation of aqueous solution.
Carbon cycling, instead of conventional oxygen cycling in chemical looping, overcomes the limitations of oxygen storage capacity of oxygen carriers and enables the reaction to proceed under relatively mild conditions. In this study, we designed a high-performance carbon-storage catalyst (Ni-Co/Al 2 O 3 ) for chemical looping conversion of CH 4 and CO 2 to H 2 and CO. The physico-chemical characterizations suggested that the Co alloyed with Ni could result in larger active metal particles and simultaneously benefit the bending of carbon deposits toward the periphery of the active sites, avoiding the quick deactivation of catalysts due to the encapsulation of the active sites by carbon deposits and generating a higher carbon capacity (23.59 vs. 14.08 mol/kg). In addition, the alloying of Co with Ni could weaken the graphitization of carbon deposits, thus facilitating the carbon elimination and catalyst regeneration in the CO 2 conversion step, strongly improving the cycling stability during long-term testing.
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