Coal-Based Branched Vicinal Diol Ethoxylates Versus Guerbet Alcohol Ethoxylates: Role of Tertiary Hydroxyl Groups

Branched surfactants exhibit a lower surface tension, excellent low defoaming performance, and better wetting ability compared with linear surfactants, making them promising for applications in industrial cleaning. In this study, 2-hexyl-1-decene (C8 olefin dimer), obtained from the dimerization of 1-octene, was used as the hydrophobe to synthesize branched nonionic surfactants via hydroxylation and ethoxylation. The hydroxylation of the C8 olefin dimer to synthesize 2-hexyldecane-1,2-diol (C8 BD) using H2O2 and HCOOH was investigated systematically. Under the optimal reaction conditions (H2O2/C8 olefin dimer molar ratio: 1.5, HCOOH/C8 olefin dimer molar ratio: 4.0, reaction time: 10 h, reaction temperature: 50 °C), the conversion of the C8 olefin dimer and selectivity toward C8 BD were found to reach 99.96 and 79.89%, respectively. Further, branched nonionic surfactants (C8 BDEn) were synthesized via ethoxylation of C8 BD with ethylene oxide and characterized using FTIR, LCMS, 1H NMR, and 13C NMR techniques. The presence of a tertiary hydroxyl group in C8 BD increases the reactivity of the primary hydroxyl group, leading to a narrower range of products and lower residual substrate content. The physicochemical properties and surface properties of C8 BDEn with different degrees of ethoxylation at various concentrations were investigated and compared with those of commercially available Guerbet alcohol polyoxyethylene ethers (C8 GAEO9 and C6 GAEO9). The results show that, compared with C8 GAEO9 and C6 GAEO9, C8 BDE6 displayed a higher surface activity with a lower equilibrium surface tension (27.14 mN·m-1), superior wettability with a smaller contact angle (39.2°), better emulsification performance with a longer emulsification time of 548 s, and excellent foaming properties (initial foam volume of 11.6 mL). This strategy of utilizing coal-based α-olefins for the synthesis of branched nonionic surfactants presents a route to prepare value-added fine chemicals from coal-based resources.

Backbone-functionalised ruthenium diphosphine complexes for catalytic upgrading of ethanol and methanol to iso-butanol

Efficient catalysts for Guerbet-type ethanol/methanol upgrading to iso-butanol have been developed via Michael addition of a variety of amines to ruthenium-coordinated dppen (1,1-bis(diphenylphosphino)ethylene). All catalysts produce over 50% iso-butanol yield with >90% selectivity in 2 h with catalyst 1 showing the best activity (74% yield after this time). The selectivity and turnover number approach 100% and 1000 respectively using catalyst 6. The presence of uncoordinated functionalised donor groups in these complexes results in a more stable catalyst compared to unfunctionalised analogues.

Recent advances in cross-coupling of alcohols via borrowing hydrogen catalysis

Application of the borrowing hydrogen strategy facilitates utilization of abundantly available alcohols for linear or branched long-chain alcohols. Selective synthesis of such alcohols is highly challenging and involves the utilization of transition metal catalysts towards the desired cross-coupled product. Herein, we have highlighted recent advances (from 2015 to 2023) towards the synthesis of higher alcohols. Major focus has been given to the development of ligands, including transition metal catalysts. Judicious catalyst design plays a key role in the alkylation process and is summarised in this review.

Upgrading Ethanol to n-Butanol in the Presence of Carbonate Catalyzed by a Cp*Ir Complex Bearing a Functional 2,2'-Carbonylbibenzimidazole Ligand

Upgrading ethanol to n-butanol as biofuels is an important topic for sustainable chemistry. Herein, a Cp*Ir complex bearing a functional 2,2'-carbonylbibenzimidazole ligand [Cp*Ir(2,2'-COBiBzImH2)Cl][Cl] was designed and synthesized. In the presence of a catalyst (0.1 mol %) and Cs2CO3 (6 mol %), the highest yield of updated n-butanol is up to 37% with 80% selectivity. NH units in the ligand are crucially important for the catalytic activity of the iridium complex.

Ruthenium-Catalyzed Self-Coupling of Secondary Alcohols

A simple catalytic method for self-coupling of secondary alcohols leading to the synthesis of β-branched ketones under mild conditions is reported. Well-defined ruthenium pincer complex catalyzed the reactions. Optimization studies revealed that sodium tert-butoxide is an appropriate base for this transformation. Functionalized aryl methanols, heteroaryl methanols, and linear and branched aliphatic secondary alcohols underwent facile catalytic self-coupling reactions. Mechanistic studies revealed that both catalyst and base are crucial to achieve dehydrogenation of secondary alcohols to ketones, their subsequent controlled aldol condensation, and further hydrogenation of α,β-unsaturated intermediates, leading to the selective formation of β-branched ketone products. Notably, the noninnocent PNP ligand which displays amine-amide metal-ligand cooperation operative in a catalyst played a key role in facilitating this catalytic self-coupling of secondary alcohols. Liberated molecular hydrogen and water are the only byproducts.

Ethanol Coupling Reactions over MgO-Al2O3 Mixed Oxide-Based Catalysts for Producing Biofuel Additives

Catalytic conversion of ethanol to 1-butanol was studied over MgO-Al₂O₃ mixed oxide-based catalysts. Relationships between acid-base and catalytic properties and the effect of active metal on the hydrogen transfer reaction steps were investigated. The acid-base properties were studied by temperature-programmed desorption of CO₂ and NH₃ and by the FT-IR spectroscopic examination of adsorbed pyridine. Dispersion of the metal promoter (Pd, Pt, Ru, Ni) was determined by CO pulse chemisorption. The ethanol coupling reaction was studied using a flow-through microreactor system, He or H₂ carrier gas, WHSV = 1 gEtOH·gcat.-1·h-1, at 21 bar, and 200-350 °C. Formation and transformation of surface species under catalytic conditions were studied by DRIFT spectroscopy. The highest butanol selectivity and yield was observed when the MgO-Al₂O₃ catalyst contained a relatively high amount of strong-base and medium-strong Lewis acid sites. The presence of metal improved the activity both in He and H₂; however, the butanol selectivity significantly decreased at temperatures ≥ 300 °C due to acceleration of undesired side reactions. DRIFT spectroscopic results showed that the active metal promoted H-transfer from H₂ over the narrow temperature range of 200-250 °C, where the equilibrium allowed significant concentrations of both dehydrogenated and hydrogenated products.

Adsorbate-Induced Strong Metal-Support Interactions: Implications for Catalyst Design

Since the discovery of strong metal-support interactions (SMSIs) over supported metal catalysts in the 1970s, researchers have studied ways to harness this type of catalyst reconstruction to achieve enhanced stability of metal particles against sintering and to create catalytic sites with novel electronic and bonding properties. The motivation to elucidate performance-structure relationships in catalytic transformations has led researchers to take a closer look into catalytic surfaces under reaction conditions rather than a postreaction analysis. These investigations of operating catalysts have made it clear that SMSIs are more common than initially thought. Recent reports show how various adsorbed species, rather than traditional H₂/O₂ treatment, can promote SMSI in various catalytic systems, a phenomenon named adsorbate-induced SMSI (A-SMSI). Researching the occurrence of A-SMSI has allowed fundamental understanding of catalyst stability, catalytic rates, and product selectivity. The present Perspective discusses the state-of-the-art regarding A-SMSI, the current challenges, and the opportunities ahead in heterogeneous catalysis.

Sustainable routes to alkenes: applications of homogeneous catalysis to the dehydration of alcohols to alkenes

Homogeneous catalysis applied to alcohol dehydration.

P,N-type phosphaalkene-based Ir(i) complexes: synthesis, coordination chemistry, and catalytic applications

Iridium P,N phosphaalkene complexes show a rich coordination chemistry with unusual twofold C–H activation. The Ir(i) chloride complex can be applied for C–N coupling and alcohol upgrading reactions.

One pot tandem dehydrogenative cross-coupling of primary and secondary alcohols by ruthenium amido-functionalized 1,2,4-triazole derived N-heterocyclic carbene complexes

One-pot tandem dehydrogenative cross-coupling of primary and secondary alcohols was catalyzed by three ruthenium complexes [1-(R)-4-N-(furan-2-ylmethyl)acetamido-1,2,4-triazol-5-ylidene]Ru(p-cymene)Cl [R = Et (1b), i-Pr (2b), Bn (3b)], of amido-functionalized 1,2,4-triazole derived N-heterocyclic carbene (NHC) ligands. Density Functional Theory (DFT) calculations were employed for the ruthenium (1b) precatalyst to understand this reaction mechanism completely, and the mechanisms adapted are divided categorically into three steps (i) nucleophilic substitution of chloride ions by alcohols, (ii) dehydrogenation of primary and secondary alcohols, and (iii) olefin and ketone hydrogenation. Our mechanistic study reveals that the formation of a deprotonated Ru-alcoholate (A) or (E) intermediate is favorable compared to the protonated form (A') or (E') from (1b) by associative nucleophilic substitution. Though an ionic pathway that proceeds through (A') or (E'), has less barriers in the dehydrogenation and olefin/ketone hydrogenation steps than that of the neutral pathway, proceeding through (A) or (E), a steep energy barrier was observed in the first nucleophilic substitution step, prohibiting the reaction to proceed via the intermediate (A') or (E'). Thus, our thorough mechanistic study reveals that the reaction proceeds via deprotonated Ru-alcoholate (A) or (E) species. Furthermore, the 1,4 addition of an α,β-unsaturated carbonyl compound is kinetically and thermodynamically favorable over the 1,2 addition, and the experiments support these observations. As a testimony towards practical application in synthesizing bio-active flavonoid based natural products, five different flavan derivatives (16-20), were synthesized by the dehydrogenative coupling reaction using the neutral ruthenium (1-3)b complexes.

Synthesis of a branched surfactant from the castor derivative and its surface properties

A new class of ricinoleic acid-derived branched surfactant with a Y-shaped structure (ethoxylated monohydroxy stearic acid methyl ester, 12-HMEE_n) was synthesized and characterized by introducing a polyoxyethylene head group in the hydroxyl position inside the molecule. The physicochemical properties and surface activities of 12-HMEE_n with different degrees of ethoxylation at various concentrations were studied. The typical Y-shaped structure of the molecule facilitates its adsorption at the interface, which provides an excellent surface activity and affects its surfactant properties significantly. The dynamic contact angle, wettability, foaming properties, and compatibility tests of 12-HMEE_n showed that it has good wetting performance, low foaming and fast defoaming properties, and good compatibility in formulation applications, indicating that the surfactant has potential application in industrial cleaning.

Tuning the selectivity in iridium-catalyzed acceptorless dehydrogenative coupling of primary alcohols

An acceptorless dehydrogenative coupling of primary alcohols to carboxylic acids/carboxylates, esters, and Guerbet alcohols (via both homo- and cross-β-alkylation of the alcohols) in the presence of an N-heterocyclic carbene iridium(I) catalyst was developed under aerobic conditions. The product selectivity can be easily tuned among the products with a single catalyst through simple modification of the reaction conditions, such as the catalyst and base amounts, the choice of base, and the reaction temperature.

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

The production of biobutanol from bioethanol by the Guerbet reaction is an alternative pathway to renewable sources. The commercial viability of this green route requires improvements in the process development. This study experimentally examines the influence of operating conditions on the performance of a Mg–Al spinel catalyst prepared from hydrotalcite precursors. This catalyst demonstrates an exceptional performance in the Guerbet reaction with a promising activity/butanol selectivity balance, excellent long-term stability, and very-low-carbon footprint (CO2 generation as by-products is minimal). This study showcases a systematic strategy to optimize the reaction parameters in the Guerbet reaction for biobutanol production using an advanced spinel catalyst. Upon carefully adjusting temperature, pressure, space velocity, and reactants co-feeding, very promising conversion (35%) and butanol selectivity values (48%) were obtained.

N,N-Dimethylformamide-stabilized ruthenium nanoparticle catalyst for β-alkylated dimer alcohol formation via Guerbet reaction of primary alcohols

N,N-Dimethylformamide-stabilized Ru nanoparticles (NPs) provide a highly efficient catalyst for the Guerbet reaction of primary alcohols. DMF-modified Ru NPs were synthesized, and characterized by transition electron microscopy, and X-ray absorption spectroscopy, X-ray photoelectronspectroscopy, and Fourier-transform infrared spectroscopy. The Ru NP catalyst was highly durable during catalytic reactions under external additive/solvent-free conditions.

Synthesis of α-Hydroxy Acids via Dehydrogenative Cross-Coupling of a Sustainable C2 Chemical (Ethylene Glycol) with Alcohols

Ir(NHC) (NHC, N-heterocyclic carbene)-catalyzed dehydrogenative coupling of sustainable ethylene glycol and various bioalcohols can produce industrially valuable α-hydroxy acids (AHAs). This study is the first to report the sustainable synthesis of higher C_n AHAs, in addition to glycolic acid (C₂ AHA) and lactic acid (C₃ AHA). This catalytic system can be recycled to the seventh cycle while maintaining good yields. A reaction mechanism, including facile dehydrogenation of each alcohol and fast cross-coupling of dehydrogenated aldehydes forming products, was proposed based on ¹⁸O- and ²H-labeling experiments and electron spray ionization-mass spectrometry (ESI-MS) and NMR spectral analyses.

Lignin Depolymerization in the Presence of Base, Hydrogenation Catalysts and Ethanol

Being the major renewable source of bio-aromatics, lignin possesses considerable potential for the chemical industry as raw material. Kraft lignin is a couple product of paper industry with an annual production of 55,000,000 ton/y and is considered the largest share of available lignin. Here we report a facile approach of Kraft lignin depolymerization to defined oligomeric units with yields of up to 70 wt.%. The process implies utilization of an aqueous base in combination with a metal containing catalyst and an alcohol under non-oxidative atmosphere at 300 °C. An advantage of the developed approach is the facile separation of the oligomer product that precipitates from the reaction mixture. In addition, the process proceeds without char formation; both factors make it attractive for industrialization. The suppression of the repolymerization processes that lead to char formation is possible when the combination of metal containing catalyst in the presence of an alcohol is used. It was found that the oligomer units have structural features found in phenol-acetaldehyde resins. These features result from the base catalyzed condensation of lignin fragments with in situ formed aldehydes. Catalytic dehydrogenation of the alcohol provides the latter. This reaction pathway is confirmed by the presence condensation products of Guerbet type reactions.

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

As the world pledges to significantly cut carbon emissions, the demand for sustainable and clean energy has now become more important than ever. This includes both production and storage of energy carriers, a majority of which involve catalytic reactions. This article reviews recent developments of homogeneous catalysts in emerging applications of sustainable energy. The most important focus has been on hydrogen storage as several efficient homogeneous catalysts have been reported recently for (de)hydrogenative transformations promising to the hydrogen economy. Another direction that has been extensively covered in this review is that of the methanol economy. Homogeneous catalysts investigated for the production of methanol from CO2, CO, and HCOOH have been discussed in detail. Moreover, catalytic processes for the production of conventional fuels (higher alkanes such as diesel, wax) from biomass or lower alkanes have also been discussed. A section has also been dedicated to the production of ethylene glycol from CO and H2 using homogeneous catalysts. Well-defined transition metal complexes, in particular, pincer complexes, have been discussed in more detail due to their high activity and well-studied mechanisms.

Mechanistic investigations on a homogeneous ruthenium Guerbet catalyst in a flow reactor

A mechanistic investigation on the ethanol self-condensation reaction (Guerbet reaction) catalyzed by a bis(pyridylimino)isoindolate Ru(ii) catalyst was performed using a specifically designed continuously-stirred tank reactor (CSTR).

Structural Evolution of MOF-Derived RuCo, A General Catalyst for the Guerbet Reaction

Guerbet alcohols, a class of β-branched terminal alcohols, find widespread application because of their low melting points and excellent fluidity. Because of the limitations in the activity and selectivity of existing Guerbet catalysts, Guerbet alcohols are not currently produced via the Guerbet reaction but via hydroformylation of oil-derived alkenes followed by aldol condensation. In pursuit of a one-step synthesis of Guerbet alcohols from simple linear alcohol precursors, we show that MOF-derived RuCo alloys achieve over a million turnovers in the Guerbet reaction of 1-propanol, 1-butanol, and 1-pentanol. The active catalyst is formed in situ from ruthenium-impregnated metal-organic framework MFU-1. XPS and XAS studies indicate that the precatalyst is composed of Ru precursor trapped inside the MOF pores with no change in the oxidation state or coordination environment of Ru upon MOF incorporation. The significantly higher reactivity of Ru-impregnated MOF versus a physical mixture of Ru precursor and MOF suggests that the MOF plays an important role in templating the formation of the active catalyst and/or its stabilization. XPS reveals partial reduction of both ruthenium and MOF-derived cobalt under the Guerbet reaction conditions, and TEM/EDX imaging shows that Ru is decorated on the edges of dense nanoparticles, as well as thin nanoplates of CoOx. The use of ethanol rather than higher alcohols as a substrate results in lower turnover frequencies, and RuCo recovered from ethanol upgrading lacks nanostructures with plate-like morphology and does not exhibit Ru-enrichment on the surface and edge sites. Notably, 1H and 31P NMR studies show that through use of K3PO4 as a base promoter in the RuCo-catalyzed alcohol upgrading, the formation of carboxylate salts, a common side product in the Guerbet reaction, was effectively eliminated.

Interfacial Sites in Ag Supported Layered Double Oxide for Dehydrogenation Coupling of Ethanol to n-Butanol

Upgrading of ethanol to n-butanol through dehydrogenation coupling has received increasing attention due to the wide application of n-butanol. But the enhancement of ethanol dehydrogenation and followed coupling to produce high selectivity to n-butanol is still highly desired. Our previous work has reported an acid-base-Ag synergistic catalysis, with Ag particles supported on Mg and Al-containing layered double oxides (Ag/MgAl-LDO). Here, Ag-LDO interfaces have been manipulated for dehydrogenation coupling of ethanol to n-butanol by tailoring the size of Ag particles and the interactions between Ag and LDO. It has been revealed that increasing the population of surface Ag sites at Ag-LDO interfaces promotes not only the dehydrogenation of ethanol to acetaldehyde but also the subsequent aldol condensation of generated acetaldehyde. A selectivity of up to 76 % to n-butanol with an ethanol conversion of 44 % has been achieved on Ag/LDO with abundant interfacial Ag sites, much superior to the state-of-the-art catalysts.

Bio-DEE Synthesis and Dehydrogenation Coupling of Bio-Ethanol to Bio-Butanol over Multicomponent Mixed Metal Oxide Catalysts

Within the Waste2Fuel project, innovative, high-performance, and cost-effective fuel production methods from municipal solid wastes (MSWs) are sought for application as energy carriers or direct drop-in fuels/chemicals in the near-future low-carbon power generation systems and internal combustion engines. Among the studied energy vectors, C1-C2 alcohols and ethers are mainly addressed. This study presents a potential bio-derived ethanol oxidative coupling in the gas phase in multicomponent systems derived from hydrotalcite-containing precursors. The reaction of alcohol coupling to ethers has great importance due to their uses in different fields. The samples have been synthesized by the co-precipitation method via layered double hydroxide (LDH) material synthesis, with a controlled pH, where the M(II)/M(III) ≈ 0.35. The chemical composition and topology of the sample surface play essential roles in catalyst activity and product distribution. The multiple redox couples Ni2+/Ni3+, Cr2+/Cr3+, Mn2+/Mn3+, and the oxygen-vacant sites were considered as the main active sites. The introduction of Cr (Cr3+/Cr4+) and Mn (Mn3+/Mn4+) into the crystal lattice could enhance the number of oxygen vacancies and affect the acid/base properties of derived mixed oxides, which are considered as crucial parameters for process selectivity towards bio-DEE and bio-butanol, preventing long CH chain formation and coke deposition at the same time.

Guerbet Reactions for Biofuel Production from ABE Fermentation Using Bifunctional Ni-MgO-Al2O3 Catalysts

To upgrade biomass-derived alcohol mixtures to biofuels under solvent-free conditions, MgO–Al2O3 mixed metal oxides (MMO) decorated with Ni nanoparticles (Ni–MgO–Al2O3) are synthesized and characterized. Based on the result, Ni nanoparticles are highly dispersed on the surface of MgAl MMO. As the Ni loading content varies from 2 to 10 wt.%, there is a slight increase in the mean Ni particle size from 6.7 to 8.5 nm. The effects of Ni loading amount, reducing temperature, and Mg/Al ratio on the conversion and product distribution are investigated. With the increase in both the Ni loading amount and reducing temperature, dehydrogenation (the first step of the entire reaction network) is accelerated. This results in an increase in the conversion process and a higher selectivity for the dialkylated compounds. Due to the higher strength and density of basic sites under high Mg/Al ratios, double alkylation is preferred and more long-chain hydrocarbons are obtained. A conversion of 89.2% coupled with a total yield of 79.9% for C5–C15 compounds is acquired by the as-prepared catalyst (prepared with Ni loading of 6 wt.%, reducing temperature of 700 °C, and Mg/Al molar ratio of 3. After four runs, the conversion drops by 17.1%, and this loss in the catalytic activity can be attributed to the decrease in the surface area of the catalyst and the increase in the Ni mean particle size.

Elucidating the Influence of the d-Band Center on the Synthesis of Isobutanol

As the search for carbon-efficient synthesis pathways for green alternatives to fossil fuels continues, an expanding class of catalysts have been developed for the upgrading of lower alcohols. Understanding of the acid base functionalities has greatly influenced the search for new materials, but the influence of the metal used in catalysts cannot be explained in a broader sense. We address this herein and correlate our findings with the most fundamental understanding of chemistry to date by applying it to d-band theory as part of an experimental investigation. The commercial catalysts of Pt, Rh, Ru, Cu, Pd, and Ir on carbon as a support have been characterized by means of SEM, EDX-mapping, STEM, XRD, N2-physisorption, and H2-chemisorption. Their catalytic activity has been established by means of c-methylation of ethanol with methanol. For all catalysts, the TOF with respect to i-butanol was examined. The Pt/C reached the highest TOF with a selectivity towards i-butanol of 89%. The trend for the TOFs could be well correlated with the d-band centers of the metal, which formed a volcano curve. Therefore, this study is another step towards the rationalization of catalyst design for the upgrading of alcohols into carbon-neutral fuels or chemical feedstock.

Cross β-alkylation of primary alcohols catalysed by DMF-stabilized iridium nanoparticles

A simple method for the cross β-alkylation of linear alcohols with benzyl alcohols in the presence of DMF-stabilized iridium nanoparticles was developed. The nanoparticles were prepared in one-step and thoroughly characterized. Furthermore, the optimum reaction conditions have a wide substrate scope and excellent product selectivity.