Catalyst Performance Studies on the Guerbet Reaction in a Continuous Flow Reactor Using Mono- and Bi-Metallic Cu-Ni Porous Metal Oxides

Abstract

Higher alcohols like 1-butanol are considered important biofuels with superior properties compared to the more readily available bio-ethanol. An attractive route to prepare 1-butanol from ethanol is the Guerbet reaction. We here report the use of hydrotalcite-derived mono- (Cu-PMO or Ni-PMO) and bi-metallic (CuNi-PMO) porous metal oxide catalysts for the Guerbet coupling of ethanol to 1-butanol in a continuous flow reactor (320 °C, 0.1 MPa, LHSV = 15 mL g−1 h−1) at extended times on stream (~160 h). Two distinct regimes with different product distributions were observed for the Cu-PMO and CuNi-PMO catalyst with time on stream. At the start of the run, the initial conversion of ethanol dropped from about 85% to less than 20% after 60 h and acetaldehyde was the main product (regime 1). At prolonged times on stream (60–160 h), fairly constant low conversions of ethanol (14%) were observed and 1-butanol was the main product (regime 2). Performance of the monometallic Cu-PMO catalyst in terms of 1-butanol yield and stability was lower compared to the bi-metallic CuNi-PMO. Detailed catalyst characterization studies (XRD, H2-TPR, sorption of acrylic acid, TGA, TEM, HAADF-STEM, and EDS mapping) on both fresh and spent CuNi-PMO taken at various times on stream was performed to determine the changes in catalyst morphology and composition during a run, and particularly to obtain information on changes in catalyst structure operating in regime 1 or 2. The change in chemoselectivity is in line with an increase in basicity of the catalyst at extended runtimes.

High Performing and Stable Cu/NiAlOx Catalysts for the Continuous Catalytic Conversion of Ethanol into Butanol

“…Furthermore, to examine the chemical state of Cu species in the serials of Cu/NiAlO x catalysts, X‐ray photoelectron spectroscopy (XPS) was conducted on the above samples. For the fresh Cu/NiAlO x catalysts, the Cu 2p 3/2 signals are observed at 934.7 and 932.9 eV, respectively, which are the characteristic peaks of Cu 2+ and reduced Cu + /Cu 0 species (Figure 6a) [10,11,44] . Cu LMM X‐ray‐induced Auger electron spectroscopy (XAES) was carried out for further discrimination and quantification of the Cu 0 and Cu + species (Figure 6b).…”

“…For the fresh Cu/NiAlO x catalysts, the Cu 2p 3/2 signals are observed at 934.7 and 932.9 eV, respectively, which are the characteristic peaks of Cu 2 + and reduced Cu + /Cu 0 species (Figure 6a). [10,11,44] Cu LMM Xray-induced Auger electron spectroscopy (XAES) was carried out for further discrimination and quantification of the Cu 0 and Cu + species (Figure 6b). The featured peaks located at 918.6 and 914.8 eV are ascribed to Cu 0 and Cu + , respectively.…”

“…[3] The catalytic upgrading of ethanol into butanol through the Guerbet coupling reaction, a well-known industrial route for higher alcohol synthesis, have attracted widespread attention recently. [10,11] A commonly proposed mechanism for this process consists of a three-step sequence of reactions, which involves an initial dehydrogenation step to form acetaldehyde, a subsequent aldol self-condensation reaction to crotonaldehyde/ butanal, and the final hydrogenation of the condensation product to butanol, as shown in Scheme 1. [12][13][14] Meanwhile, a variety of byproducts, such as ethene, ether, ethyl acetate, hexanol, etc., might be also produced from the competitive side-reaction owing to the complicated process.…”

Boosting the C–C Coupling of Bioethanol to Higher Alcohols by Inhibiting Aqueous Phase Reforming Reaction

“…Guerbet reaction is a well-known approach to convert short-chain primary alcohols into higher alcohols, which includes an initial dehydrogenation of short-chain primary alcohols to form the corresponding aldehydes followed by aldol condensation and hydrogenation to form higher alcohols. − A suitable catalyst with an exact match of the acidity/basicity, ingenious geometric structure, and proper electronic environment is vital for the Guerbet reaction. , Generally, the metal sites catalyze the steps of dehydrogenation and hydrogenation, while the acid–base sites selectively catalyze the steps of dehydration and aldol condensation. , …”

Insights on Guerbet Reaction: Production of Biobutanol From Bioethanol Over a Mg–Al Spinel Catalyst

“…In addition, long-term tests are necessary to validate industrial operations. In the literature, Xi et al (2020 ) carried out a catalytic test which lasted 160 h, but most of the published articles performed short-term trials. For instance, Cimino et al (2018) tested a Ru/MgO catalyst for only 6 h. Under this scenario, the aim of this work is to study the effect of operating conditions in the performance of a Mg–Al spinel catalyst prepared from hydrotalcite precursors, for the direct synthesis of butanol from ethanol.…”