Selective Hydrogenation of Polyenes in Biomass-Derived Cardanol over the Trimetallic Ni–Co–Cu Catalyst Supported on Morphologically Controlled Alumina
The aim of this study is to achieve a high fraction of monoene in biomass-derived cardanol to manipulate a well-balanced potential of cross-linking and coupling between resin and curing agent for heavy-duty coating. We reported a heterogeneous nonprecious trimetallic catalyst for selective hydrogenation of polyenes in cardanol for the first time. By cointroducing the second and third metal constituents (Cu and Co), and particularly facet controlling as well as Zn doping of Al2O3 substrate, we can accomplish the highly selective hydrogenation of triene/diene into monoene with variable ratio. The larger sized Ni entities with higher electron density on the Al2O3 hexagonal plates are more favorable for activating triene/diene responsible for a high potential of selective hydrogenation. On the other hand, the Ni0 fraction is comparatively lower, while the mean particle size of Ni0 is the smallest with lower electron density on the commercially obtained γ-Al2O3 spherules. The latter kind of Ni entities is more favorable for activating hydrogen to generate highly reactive H species accounting for a strong potential of full hydrogenation. Over a fine-tuned 10% Ni-5% Co-3% Cu/3% Zn-Al2O3-hexagonal plate under the optimized conditions (7.5% cardanol in n-butanol, 2.5 MPa H2, 80 °C, and 3.5 h), as high as 76% monoene can be obtainable. It is worth noting that not only the current catalyst system is more economic but also the reaction becomes kinetically much faster (within 3.5 h). This catalyst system is operational to a large-scale application in the modification of cardanol via selective hydrogenation. Ni–Co–Cu synergism and low-content Zn modification of the Al2O3 (110) facet are essential to achieve the aim of this study.
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