Optimization of Cu-Ni-Mn-catalysts for the conversion of ethanol to butanol

State-of-the-art advances in homogeneous molecular catalysis for the Guerbet upgrading of bio-ethanol to fuel-grade bio-butanol

The upgrading of ethanol to n-butanol marks a major breakthrough in the field of biofuel technology, offering the advantages of compatibility with existing infrastructure while simultaneously offering potential benefits in terms of transport efficiency and energy density. With its lower vapour pressure and reduced corrosiveness compared to ethanol, n-butanol is easier not only to manage but also to transport, eliminating the need for costly infrastructure changes. This leads to improved fuel efficiency and reduced fuel consumption. These features position n-butanol as a promising alternative to ethanol in the future of biodiesel. This review article delves into the cutting-edge advancements in upgrading ethanol to butanol, highlighting the critical importance of this transformation in enhancing the value and practical application of biofuels. While traditional methods for making butanol rely heavily on fossil fuels, those that employ ethanol as a starting material are dominated by heterogeneous catalysis, which is limited by the requirement of high temperatures and a lack of selectivity. Homogeneous catalysts have been pivotal in enhancing the efficiency and selectivity of this conversion, owing to their unique mode of operation at the molecular level. A comprehensive review of the various homogeneous catalytic processes employed in the transformation of feedstock-agnostic bio-ethanol to fuel-grade bio-n-butanol is provided here, with a major focus on the key advancements in catalyst design, reaction conditions and mechanisms that have significantly improved the efficiency and selectivity of these Guerbet reactions.

Ni-Based Hydrotalcite (HT)-Derived Cu Catalysts for Catalytic Conversion of Bioethanol to Butanol

Catalytic conversion of biomass-derived ethanol into n-butanol through Guerbet coupling reaction has become one of the key reactions in biomass valorization, thus attracting significant attention recently. Herein, a series of supported Cu catalysts derived from Ni-based hydrotalcite (HT) were prepared and performed in the continuous catalytic conversion of ethanol into butanol. Among the prepared catalysts, Cu/NiAlOx shows the best performance in terms of butanol selectivity and catalyst stability, with a sustained ethanol conversion of ~35% and butanol selectivity of 25% in a time-on-stream (TOS) of 110 h at 280 °C. While for the Cu/NiFeOx and Cu/NiCoOx, obvious catalyst deactivation and/or low butanol selectivity were obtained. Extensive characterization studies of the fresh and spent catalysts, i.e., X-ray diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Hydrogen temperature-programmed reduction (H2-TPR), reveal that the catalysts' deactivation is mainly caused by the support deconstruction during catalysis, which is highly dependent on the reducibility. Additionally, an appropriate acid-base property is pivotal for enhancing the product selectivity, which is beneficial for the key process of aldol-condensation to produce butanol.

NiFeMn-Layered Double Hydroxides Linked by Graphene as High-Performance Electrocatalysts for Oxygen Evolution Reaction

Currently, precious metal group materials are known as the efficient and widely used oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts. The exorbitant prices and scarcity of the precious metals have stimulated scale exploration of alternative non-precious metal catalysts with low-cost and high performance. Layered double hydroxides (LDHs) are a promising precursor to prepare cost-effective and high-performance catalysts because they possess abundant micropores and nitrogen self-doping after pyrolysis, which can accelerate the electron transfer and serve as active sites for efficient OER. Herein, we developed a new highly active NiFeMn-layered double hydroxide (NFM LDH) based electrocatalyst for OER. Through building NFM hydroxide/oxyhydroxide heterojunction and incorporation of conductive graphene, the prepared NFM LDH-based electrocatalyst delivers a low overpotential of 338 mV at current density of 10 mA cm⁻² with a small Tafel slope of 67 mV dec⁻¹, which are superior to those of commercial RuO₂ catalyst for OER. The LDH/OOH heterojunction involves strong interfacial coupling, which modulates the local electronic environment and boosts the kinetics of charge transfer. In addition, the high valence Fe³⁺ and Mn³⁺ species formed after NaOH treatment provide more active sites and promote the Ni²⁺ to higher oxidation states during the O₂ evolution. Moreover, graphene contributes a lot to the reduction of charge transfer resistance. The combining effects have greatly enhanced the catalytic ability for OER, demonstrating that the synthesized NFM LDH/OOH heterojunction with graphene linkage can be practically applied as a high-performance electrocatalyst for oxygen production via water splitting.

Potentials of bio-butanol conversion to valuable products

In the last decade, there was observed a growing demand for both n-butanol as a potential fuel or fuel additive, and propylene as the only raw material for production of alcohol and other more bulky propylene chemical derivatives with faster growing outputs (polymers, propylene oxide, and acrylic acid). The predictable oilfield depletion and the European Green Deal adoption stimulated interest in alternative processes for n-butanol production, especially those involving bio-based materials. Their commercialization will promote additional market penetration of n-butanol for its application as a basic chemical. We analyze briefly the current status of two most advanced bio-based processes, i.e. ethanol–to-n-butanol and acetone–butanol–ethanol (ABE) fermentation. In the second part of the review, studies of n-butanol and ABE conversion to valuable products are considered with an emphasis on the most perspective catalytic systems and variants of the future processes realization.

Eco-Friendly and Sustainable Process for Converting Hydrous Bioethanol to Butanol

The purpose of the study was the development of water-resistant catalyst and catalytic processes for the conversion of hydrous ethanol to 1-butanol. Water, in hydrous ethanol, strongly inhibits conversion to 1-butanol on solid catalysts. In this study, the nonstoichiometric P-deficient hydroxyapatite containing carbonate anions (C-HAP), Ca10−x/2(PO4)6−x(CO3)x(OH)2, displayed good performance in the Guerbet condensation of hydrated ethanol to 1-butanol, after proper stabilization of reaction conditions. Hydrous ethanol (96 wt%) was converted on C-HAP formed as extrudates with silica binder at 400 °C and weight hour space velocity (WHSV) = 0.5–1.0 h−1 to yield 21–23% 1-butanol and 73–74% selectivity. It displayed stable operation for up to 170 h on streams conducted in bench and mini-pilot rigs with catalyst loadings of 2 and 50 cm3, respectively. The process simulation employed the recycling of ethanol without laboratory verification to reach 68% theoretical yield of 1-butanol. The techno-economic analysis demonstrated the feasibility of this process, showing that it may be profitable depending on the prices of hydrated ethanol and 1-butanol.