From sugars to aliphatic amines: as sweet as it sounds? Production and applications of bio-based aliphatic amines

Aliphatic amines encompass a diverse group of amines that include alkylamines, alkyl polyamines, alkanolamines and aliphatic heterocyclic amines. Their structural diversity and distinctive characteristics position them as indispensable components across multiple industrial domains, ranging from chemistry and technology to agriculture and medicine. Currently, the industrial production of aliphatic amines is facing pressing sustainability, health and safety issues which all arise due to the strong dependency on fossil feedstock. Interestingly, these issues can be fundamentally resolved by shifting toward biomass as the feedstock. In this regard, cellulose and hemicellulose, the carbohydrate fraction of lignocellulose, emerge as promising feedstock for the production of aliphatic amines as they are available in abundance, safe to use and their aliphatic backbone is susceptible to chemical transformations. Consequently, the academic interest in bio-based aliphatic amines via the catalytic reductive amination of (hemi)cellulose-derived substrates has systematically increased over the past years. From an industrial perspective, however, the production of bio-based aliphatic amines will only be the middle part of a larger, ideally circular, value chain. This value chain additionally includes, as the first part, the refinery of the biomass feedstock to suitable substrates and, as the final part, the implementation of these aliphatic amines in various applications. Each part of the bio-based aliphatic amine value chain will be covered in this Review. Applying a holistic perspective enables one to acknowledge the requirements and limitations of each part and to efficiently spot and potentially bridge knowledge gaps between the different parts.

Unveiling Highly Sensitive Active Site in Atomically Dispersed Gold Catalysts for Enhanced Ethanol Dehydrogenation

Developing a desirable ethanol dehydrogenation process necessitates a highly efficient and selective catalyst with low cost. Herein, we show that the "complex active site" consisting of atomically dispersed Au atoms with the neighboring oxygen vacancies (Vo) and undercoordinated cation on oxide supports can be prepared and display unique catalytic properties for ethanol dehydrogenation. The "complex active site" Au-Vo-Zr3+ on Au1/ZrO2 exhibits the highest H2 production rate, with above 37,964 mol H2 per mol Au per hour (385 g H2 g Au - 1 ${{\rm{g}}_{{\rm{Au}}}^{ - 1} }$  h-1) at 350 °C, which is 3.32, 2.94 and 15.0 times higher than Au1/CeO2, Au1/TiO2, and Au1/Al2O3, respectively. Combining experimental and theoretical studies, we demonstrate the structural sensitivity of these complex sites by assessing their selectivity and activity in ethanol dehydrogenation. Our study sheds new light on the design and development of cost-effective and highly efficient catalysts for ethanol dehydrogenation. Fundamentally, atomic-level catalyst design by colocalizing catalytically active metal atoms forming a structure-sensitive "complex site", is a crucial way to advance from heterogeneous catalysis to molecular catalysis. Our study advanced the understanding of the structure sensitivity of the active site in atomically dispersed catalysts.

A Theoretical Study on the Mechanisms Involved in Catalytic Dehydrogenation and Dehydration of Isopropanol on SrTiO3

The dehydrogenation and dehydration of isopropanol on the SrO and TiO2 terminated surfaces, of the SrTiO3 perovskite, is addressed by periodic DFT calculations in order to shed light on the involved mechanisms. The results show that the dehydrogenation occurs through a mechanism involving the dissociative adsorption of the alcohol on the SrO terminated surface, followed the nucleophilic attack of a hydride species on the previously adsorbed hydrogen atom to form molecular hydrogen and the corresponding carbonyl compound. The dehydration instead occurs by the molecular adsorption of the alcohol on the TiO2 terminated surface, followed by various possible E1 elimination pathways leading to the formation of the corresponding alkene and a water molecule. The article reports a thorough study on the involved mechanisms, including identification of the transition states and intermediates along the reaction paths, and evaluation of the respective activation barriers, as well. Thus, this article provides significant insights about the mechanisms of dehydrogenation and dehydration of isopropanol on the SrTiO3 , not reported earlier in literature. The calculated barrier energies are in good agreement with experimental values.

Promoted hydrogen and acetaldehyde production from alcohol dehydrogenation enabled by electrochemical hydrogen pumps

The dehydrogenation reaction of bioderived ethanol is of particular interest for the synthesis of fuels and value-added chemicals. However, this reaction historically suffered from high energy consumption (>260 °C or >0.8 V) and low efficiency. Herein, the efficient conversion of alcohol to hydrogen and aldehyde is achieved by integrating the thermal dehydrogenation reaction with electrochemical hydrogen transfer at low temperature (120 °C) and low voltage (0.06 V), utilizing a bifunctional catalyst (Ru/C) with both thermal-catalytic and electrocatalytic activities. Specifically, the coupled electrochemical hydrogen separation procedure can serve as electrochemical hydrogen pumps, which effectively promote the equilibrium of ethanol dehydrogenation toward hydrogen and acetaldehyde production and simultaneously purifies hydrogen at the cathode. By utilizing this strategy, we achieved boosted hydrogen and acetaldehyde yields of 1,020 mmol g-1 h-1 and 1,185 mmol g-1 h-1, respectively, which are threefold higher than the exclusive ethanol thermal dehydrogenation. This work opens up a prospective route for the high-efficiency production of hydrogen and acetaldehyde via coupled thermal-electrocatalysis.

A Recent Review of Primary Hydrogen Carriers, Hydrogen Production Methods, and Applications

Hydrogen is a promising energy carrier, especially for transportation, owing to its unique physical and chemical properties. Moreover, the combustion of hydrogen gas generates only pure water; thus, its wide utilization can positively affect human society to achieve global net zero CO2 emissions by 2050. This review summarizes the characteristics of the primary hydrogen carriers, such as water, methane, methanol, ammonia, and formic acid, and their corresponding hydrogen production methods. Additionally, state-of-the-art studies and hydrogen energy applications in recent years are also included in this review. In addition, in the conclusion section, we summarize the advantages and disadvantages of hydrogen carriers and hydrogen production techniques and suggest the challenging tasks for future research.

Preparation of core-shell catalyst for the tandem reaction of amino compounds with aldehydes

Heterogeneous noble metal-based catalysts with stable, precise structures and high catalytic performance are of great research interest for sustainable catalysis. In this article, we designed a novel core-shell catalyst, Pd@UiO-66-NH₂@mSiO₂, with Pd@UiO-66-NH₂ as the core and mesoporous SiO₂ (mSiO₂) as the shell. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) measurement results demonstrated that the obtained catalyst has an excellent core-shell structure. It can significantly prevent the aggregation of Pd nanoparticles (NPs), as well as the leaching of Pd NPs during the reaction process, owing to the protective effect of mSiO₂. During the tandem reaction of aniline and benzaldehyde to generate secondary amines, the prepared Pd@UiO-66-NH₂@mSiO₂ is highly efficient, due to the strong acid sites provided by UiO-66-NH₂ and the hydrogenation reduction sites provided by Pd NPs. Meanwhile, the Pd@UiO-66-NH₂@mSiO₂ with porous structure can also enhance the mass transfer of reactants to improve the reaction efficiency. Additionally, the prepared catalyst was used to catalyze the series reaction of amino compounds and aldehydes, and the results showed that just 5 mg of the catalyst can convert more than 99% of the reactants within 60 minutes in the presence of 1 atm H₂ at room temperature. Finally, the selectivity and stability of the as-prepared catalyst were also confirmed.

Uniformly Dispersed Cu Nanoparticles over Mesoporous Silica as a Highly Selective and Recyclable Ethanol Dehydrogenation Catalyst

Selective dehydrogenation of ethanol to acetaldehyde has been considered as an important pathway to produce acetaldehyde due to the atom economy and easy separation of acetaldehyde and hydrogen. Copper catalysts have attracted much attention due to the high activity of Cu species in O-H and C-H bonds oxidative cleavage, and low process cost; however, the size of the Cu nanoparticle is difficult to control since it is easily suffers from metal sintering at high temperatures. In this work, the Cu/KIT-6 catalyst exhibited an ultra-high metal dispersion of 62.3% prepared by an electrostatic adsorption method, due to the advantages of the confinement effect of mesoporous nanostructures and the protective effect of ammonia water on Cu nanoparticles. The existence of an oxidation atmosphere had a significant effect on the valence state of copper species and enhancing moderate acid sites. The catalyst treated by reduction and then oxidation possessed a moderate/weak acid site ratio of ~0.42 and a suitable proportion of Cu+/Cu0 ratio of ~0.53, which conceivably rendered its superior ethanol conversion of 96.8% and full acetaldehyde selectivity at 250 °C. The catalyst also maintained a high selectivity of >99% to acetaldehyde upon time-on-stream of 288 h.

Insight and Activation Energy Surface of the Dehydrogenation of C2HxO Species in Ethanol Oxidation Reaction on Ir(100)

Dehydrogenation of an organic compound is the first and the most fundamental elementary reaction in many organic reactions. In ethanol oxidation reaction (EOR) to form CO 2 , there are a total of 46 pathways in C 2 H x O (x=1-6) species leading to the removal of all six hydrogen atoms in five C-H bonds and one O-H bond. To investigate the degree of dehydrogenation in EOR under operando conditions, we performed density function theory (DFT) calculations to study 28 dehydrogenation steps of C 2 H x O on Ir(100). An activation energy surface was then constructed and compared with that of the C-C bond cleavages to understand the importance of the degree of dehydrogenation in EOR. The results show that there are likely 28 dehydrogenations in EOR under fuel cell temperatures and the last two hydrogens in C 2 H 2 O are less likely cleaved. On the other hand, deep dehydrogenation including 45 dehydrogenations can occur under ethanol steam reforming conditions.

The Route from Green H2 Production through Bioethanol Reforming to CO2 Catalytic Conversion: A Review

Currently, a progressively different approach to the generation of power and the production of fuels for the automotive sector as well as for domestic applications is being taken. As a result, research on the feasibility of applying renewable energy sources to the present energy scenario has been progressively growing, aiming to reduce greenhouse gas emissions. Following more than one approach, the integration of renewables mainly involves the utilization of biomass-derived raw material and the combination of power generated via clean sources with conventional power generation systems. The aim of this review article is to provide a satisfactory overview of the most recent progress in the catalysis of hydrogen production through sustainable reforming and CO2 utilization. In particular, attention is focused on the route that, starting from bioethanol reforming for H2 production, leads to the use of the produced CO2 for different purposes and by means of different catalytic processes, passing through the water–gas shift stage. The newest approaches reported in the literature are reviewed, showing that it is possible to successfully produce “green” and sustainable hydrogen, which can represent a power storage technology, and its utilization is a strategy for the integration of renewables into the power generation scenario. Moreover, this hydrogen may be used for CO2 catalytic conversion to hydrocarbons, thus giving CO2 added value.

Size and surface-energy dependence of the adsorption/desorption equilibrium in ethanol electro-oxidation by Pd-nanoparticles. Theory and experiment

The relation between current and voltage in the electro-oxidation of ethanol by metal nanoparticles depends on experimental parameters like the applied potential, peak potential, temperature, the electron-transfer coefficient, and the number of molecules adsorbed at active sites on the nanoparticle surface. In this form, the oxidation current depends on the ability of the nanoparticles to adsorb the ethanol molecules. Though the Laviron model well describes this phenomenology, few studies focus on the dependence of the oxidation current on the size and surface properties of the metal nanoparticles. Here, we present an experimental and theoretical study that comprises the synthesis of palladium-based nanoparticles and the generalization of the Laviron model that allows determining the dependence of the oxidation current on the size, surface energy, and adsorption-desorption properties of the nanoparticles for the ethanol oxidation. The determination of the adsorption-desorption equilibrium and the electro-oxidation current dependence with the physicochemical properties of the materials was carried out by electrochemical characterization.

Photodehydrogenation of Ethanol over Cu2O/TiO2 Heterostructures

The photodehydrogenation of ethanol is a sustainable and potentially cost-effective strategy to produce hydrogen and acetaldehyde from renewable resources. The optimization of this process requires the use of highly active, stable and selective photocatalytic materials based on abundant elements and the proper adjustment of the reaction conditions, including temperature. In this work, Cu₂O-TiO₂ type-II heterojunctions with different Cu₂O amounts are obtained by a one-pot hydrothermal method. The structural and chemical properties of the produced materials and their activity toward ethanol photodehydrogenation under UV and visible light illumination are evaluated. The Cu₂O-TiO₂ photocatalysts exhibit a high selectivity toward acetaldehyde production and up to tenfold higher hydrogen evolution rates compared to bare TiO₂. We further discern here the influence of temperature and visible light absorption on the photocatalytic performance. Our results point toward the combination of energy sources in thermo-photocatalytic reactors as an efficient strategy for solar energy conversion.