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

Abstract

A suitable catalyst with an exact match of the acidity/basicity, ingenious geometric structure, and proper electronic environment is vital to the Guerbet reaction for the synthesis of C6+ higher alcohols. Herein, we synthesized a series of Ni/MgAlO and NiSn/MgAlO catalysts based on hydrotalcite laminate for one-pot upgrading of aqueous bioethanol to C6+ higher alcohols. Through the introduction of Sn to form NiSn alloys, the Ni–Ni interactions were attenuated and the cleavage of C–C bonds was suppressed with a yield of 21.9% of C6+ higher alcohols at 250 °C. Meanwhile, by precisely adjusting the ratio of the metal cation Mg2+ to Al3+, the acidity and basicity of the catalysts were optimized and Ni/(4-Mg)AlO with an optimal ratio of 4 presented a considerable C6+ alcohol yield (25.2%) at even 220 °C, as well as an impressive ethanol conversion of 67.7%. Such an excellent activity achieved at lower temperature was attributed to highly dispersed Ni metal with a Ni(Mg)O solid solution structure, leading to the enormously inhibited aqueous ethanol reforming process and significant increased yield of higher alcohols. The results reveal that the electronic structure and coordination environment of metal sites as well as higher moderately basic and strong acid sites were demonstrated to be beneficial for carbon-chain extension of higher alcohols and ethanol selectivity for dehydrogenation/hydrogenation. Moreover, the number of metal, acid, and base sites should be balanced to inhibit side reactions.

Ultra-low temperature direct reconstruction of biomass fermentation of ethanol to higher alcohols in water over thermostable hcp-Ni

“…17,18 However, high reaction temperatures above 200 °C are quite necessary for traditional Ni catalysts to achieve the desired higher alcohol selectivity (>80%) and ethanol conversion (>40%). [17][18][19][20][21][22][23][24][25] Unfortunately, the high reaction temperature not only causes excessive energy consumption and harsh conditions for bio-fermentation combined applications, but also facilitates C-C cleavage side reactions such as ethanol reforming, 26 which produce undesired C1 gaseous by-products and lead to low carbon atom economics towards higher alcohols.…”

High value-added fuel additive production from waste bio-glycerol over a versatile nanohybrid catalyst

“…32,33 MgAloxide is a well-known catalyst usually used for the Guerbet reaction due to its high moisture tolerance, mesoporous structure, and exact match of the acidity/basicity. 34 However, according to the literature survey, the composite Mg-Al derived oxides/ZSM-5 have been explored only for the formation of HMF from glucose 35 and bio-oil production from pyrolysis of natural algae/cyanobacteria 36,37 due to their highly desirable catalytic activity such as high surface area, high porosity, and possessing both acidity and basicity. At this juncture, a catalyst possessing the combination of acido-basic sites along with appropriate porosity is highly desirable for the effective production of solketal from glycerol.…”

Upgrading of Aqueous Ethanol to Long-Chain Alcohols over Immobilized Highly Dispersed Ni–Re Catalyst

“…13−16 Nickel is particularly attractive because of its widespread use and low cost. 17 However, Ni tends to dehydrogenate deeply to produce C1 gaseous products (CH 4 , CO, CO 2 , etc. ), which prevents intermediate aldehydes from being upgraded to long-chain alcohols.…”

“…Finally, the aldehyde is hydrogenated to a saturated alcohol . Since intermolecular hydrogen transfer is considered necessary for the conversion of aldols in Guerbet chemistry, the Guerbet reaction can be accelerated by adding precious or transition metals with excellent dehydrogenation properties and hydrogen transfer capabilities, such as Ir, Pd, Ru, Rh, Cu, or Ni. − Nickel is particularly attractive because of its widespread use and low cost . However, Ni tends to dehydrogenate deeply to produce C1 gaseous products (CH 4 , CO, CO 2 , etc.…”