Aqueous Phase Catalytic Conversion of Ethanol to Higher Alcohols over NiSn Bimetallic Catalysts Encapsulated in Nitrogen-Doped Biorefinery Lignin-Based Carbon

Abstract

An efficient and stable catalyst to produce higher alcohols with a higher heat value and cetane number and less corrosive to engines from aqueous ethanol is still facing challenges. Here, a novelty of NiSn bimetallic catalysts encapsulated in a nitrogen-doped lignin-based carbon material (NiSn@NC) was prepared by modified biorefinery lignin and further precisely coordinated with metal ions to form a lignin-metal supramolecular material followed by in situ calcining. Results showed that the optimized Ni20Sn1@NC catalyst exhibited a superior ethanol conversion (68.5%), a C4+ higher alcohol yield of 31.8%, and a ratio of iso to normal alcohol of 0.52. Moreover, it also exhibited excellent stability even after four-cycle runs. Structural analysis revealed that the Sn/N-doping lignin-based carbon material improved the Ni dispersion and basic site density, which adjusted efficiently the electronic structure of the metallic active site. Therefore, the NiSn@NC bimetallic catalysts showed satisfactory conversion and stability of aqueous ethanol upgrading to C4+ higher alcohols.

Efficient Catalytic Upgrading of Ethanol to Higher Alcohols via Inhibiting C–C Cleavage and Promoting C–C Coupling over Biomass-Derived NiZn@NC Catalysts

“…Hysteresis loops in the P / P 0 range of 0.4–1.0 are present in the nitrogen adsorption and desorption isotherms, corresponding to isothermal hysteresis loops of type H1 . This indicates the presence of a mesoporous network in the carbon produced from lignin, with a relatively broad range of pore size distribution and a more homogeneous particle size, which confirms the SEM and TEM results of the Ni 20 Zn 1 @NC catalyst, further demonstrating that metals are effectively dispersed by carboxymethylated and aminated lignin derivatives . The pore size distribution diagram confirms that the pore channels of the catalysts have microporous–mesoporous–macroporous hierarchical multilevel pores, which would facilitate the adsorption of ethanol and intermediates on the catalyst and increase the mass-transfer rate …”

“…43 This indicates the presence of a mesoporous network in the carbon produced from lignin, with a relatively broad range of pore size distribution and a more homogeneous particle size, which confirms the SEM and TEM results of the Ni 20 Zn 1 @NC catalyst, further demonstrating that metals are effectively dispersed by carboxymethylated and aminated lignin derivatives. 27 The pore size distribution diagram confirms that the pore channels of the catalysts have microporous−mesoporous−macroporous hierarchical multilevel pores, which would facilitate the adsorption of ethanol and intermediates on the catalyst and increase the mass-transfer rate. 44 To further investigate the graphitization state of the NiZn@ NC catalyst and the extent of defects in the graphitic carbon layer, Raman spectroscopy was performed (Figure 2c,f).…”

“…). , These abundant functional groups facilitate the modification of lignin through effective coordination and dispersion of metals by forming a lignin–metal framework and further in situ reduction and carbonization to form the metallic catalyst encapsulated and embedded by the carbon carrier, which can exploit the synergy between the metal and protective carbon layer to enhance the catalytic activity and stability . Additionally, nitrogen in situ doping through lignin amination leads to product pyridinic-N and graphitic-N, as well as abundant edge-defect structures, that can improve the interaction and dispersion between the active metals and the carbon carrier. − …”

In situ coupling of lignin‐derived carbon‐encapsulated CoFe‐CoxN heterojunction for oxygen evolution reaction

“…40,41 Furthermore, lignin-derived carbon has recently been reported as the catalyst support in the applications of electrocatalysis, 42,43 photocatalysis degradation, 44,45 Fischer-Tropsch synthesis, 46 and other fields. 47,48 However, most lignin-derived carbon catalysts are prepared using the direct carbonization of lignin followed by the impregnation of metal active ingredients, which are easily dissoluble and difficult to effectively inhibit their agglomeration, resulting in the inferior activity, and durability. 49 In this study, the inherent properties and abundant carboxyl/ hydroxyl functional groups of lignin biomacromolecule were used to precisely coordinate with transition metal ions Co 2+ and Fe 3+ using an aqueous self-assembly process to form lignin-metals complex, which were then co-doped with nitrogen precursor urea in situ…”

“…Additionally, with a three‐dimensional network structure formed by phenylpropane units, lignin is rich in phenolic hydroxyl groups, alcoholic hydroxyl groups and part of carboxyl groups, and its carbon content is as high as 60% 40,41 . Furthermore, lignin‐derived carbon has recently been reported as the catalyst support in the applications of electrocatalysis, 42,43 photocatalysis degradation, 44,45 Fischer‐Tropsch synthesis, 46 and other fields 47,48 . However, most lignin‐derived carbon catalysts are prepared using the direct carbonization of lignin followed by the impregnation of metal active ingredients, which are easily dissoluble and difficult to effectively inhibit their agglomeration, resulting in the inferior activity, and durability 49…”