Selective direct oxidation of 1-butanol into acetal using hydrogen peroxide and Cs5MPW11(H2O)O39 (M=Fe, Co, Cu) catalysts

Direct catalytic oxidation of alcohols to acetals in one step process is very attractive, because the two steps process leads firstly to aldehydes, which are unstable species serving as reactive intermediates to generate several by-products reducing process efficiency and selectivity. In this work, a new selective catalytic acetalization of 1-butanol into 1-1-dibutoxybutane acetal using H2O2 in one step process is investigated using Keggin-type polyoxometalates catalysts. The materials developed consisted of new lacunary phophotungstate salts Cs5MPW11(H2O)O39 (M=Fe, Co and Cu) which were prepared by inorganic solution condensation method and characterized using XRD, IR, SEM and EDX analysis to verify their structure, surface morphology and chemical composition. Cs5CuPW11(H2O)O39 catalyst allowed the highest performance for the oxidation of 1-butanol at 60 °C using H2O2 excess with a yield approaching 92 % and a turnover number of 784. Such activity is related to a bifunctional behavior of the catalyst as superacid and redox operating system and the synergistic effect created between the [PW11O39]7- Keggin framework, Cs+ and Cu2+.

Effective Photocatalytic Ethanol Reforming into High-Value-Added Multicarbon Compound Coupled with H2 Production Over Pt-S3 Sites at PtSA-ZnIn2S4 Interface

Selective photocatalytic production of high-value acetaldehyde concurrently with H2 from bioethanol is an appealing approach to meet the urgent environment and energy issues. However, the difficult ethanol dehydrogenation and insufficient active sites for proton reduction within the catalysts, and the long spatial distance between these two sites always restrict their catalytic activity. Here, guided by the strong metal-substrate interaction effect, an atomic-level catalyst design strategy to construct Pt-S3 single atom on ZnIn2S4 nanosheets (PtSA-ZIS) is demonstrated. As active center with optimized H adsorption energy to facilitate H2 evolution reaction, the unique Pt single atom also donates electrons to its neighboring S atoms with electron-enriched sites formed to activate the O─H bond in *CH3CHOH and promote the desorption of *CH3CHO. Thus, the synergy between Pt single atom and ZIS together will reduce the energy barrier for the ethanol oxidization to acetaldehyde, and also narrow the spatial distance for proton mass transfer. These features enable PtSA-ZIS photocatalyst to produce acetaldehyde with a selectivity of ≈100%, which will spontaneously transform into 1,1-diethoxyethane via acetalization to avoid volatilization. Meanwhile, a remarkable H2 evolution rate (184.4 µmol h-1) is achieved with a high apparent quantum efficiency of 10.50% at 400 nm.

Creating and Stabilizing an Oxidized Pd Surface under Reductive Conditions for Photocatalytic Hydrogenation of Aromatic Carbonyls

Photocatalysis provides an eco-friendly route for the hydrogenation of aromatic carbonyls to O-free aromatics, which is an important refining process in the chemical industry that is generally carried out under high pressure of hydrogen at elevated temperatures. However, aromatic carbonyls are often only partially hydrogenated to alcohols, which readily desorbs and are hardly further deoxygenated under ambient conditions. Here, we show that by constructing an oxide surface over the Pd cocatalyst supported on graphitic carbon nitride, an alternative hydrogenation path of aromatic carbonyls becomes available via a step-wise acetalization and hydrogenation, thus allowing efficient and selective production of O-free aromatics. The PdO surface allows for optimum adsorption of reactants and intermediates and rapid abstraction of hydrogen from the alcohol donor, favoring fast acetalization of the carbonyls and their consecutive hydrogenation to O-free hydrocarbons. The photocatalytic hydrogenation of benzaldehyde into toluene shows a high selectivity of >90% and a quantum efficiency of ∼10.2% under 410 nm irradiation. By adding trace amounts of HCl to the reaction solution, the PdO surface remains stable and active for long-term operation at high concentrations, offering perspective for practical applications.

Hydrogen Bonding Promotes Alcohol C-C Coupling

Photocatalytic C-C bond formation coupled with H₂ production provides a sustainable approach to producing carbon-chain-prolonged chemicals and hydrogen energy. However, the involved radical intermediates with open-shell electronic structures are highly reactive, experiencing predominant oxidative or reductive side reactions in semiconductors. Herein, we demonstrate that hydrogen bonding on the catalyst surface and in the bulk solution can inhibit oxidation and reverse reaction of α-hydroxyethyl radicals (αHRs) in photocatalytic dehydrocoupling of ethanol over Au/CdS. Intentionally added water forms surface hydrogen bonds with adsorbed αHRs and strengthens the hydrogen bonding between αHRs and ethanol while maintaining the flexibility of radicals in solution, thereby allowing for αHRs' desorption from the Au/CdS surface and their stabilization by a solvent. The coupling rate of αHR increases by 2.4-fold, and the selectivity of the target product, 2,3-butanediol (BDO), increases from 37 to 57%. This work manifests that nonchemical bonding interactions can steer the reaction paths of radicals for selective photocatalysis.

Acetal photocatalytic formation from ethanol in the presence of TiO2 rutile and anatase

The decomposition of ethanol, one of the most important biomass platform molecules, was investigated under green conditions, ambient temperature, atmospheric pressure and air for the synthesis of acetal in the presence of TiO₂ activated under UV-A radiation. The impact of ethanol concentration, of the nature of TiO₂ (rutile, anatase or mixture), of the photo-deposition of Pt under air or argon were all factors under investigation. Whatever the conditions and the nature of catalyst used, acetaldehyde was initially formed before reacting with ethanol to form acetal, a promising fuel additive. However, the subsequent generation of acetal differs depending on the conditions and the nature of catalyst. In the absence of a noble metal, rutile TiO₂ leads to an increase in acetal formation at equivalent acetaldehyde formation. This behavior is discussed considering the acidic and basic properties of rutile and anatase phases together with H⁺ generated under UV. In the presence of Pt, under air or Ar, the acetal formation begins at a lower concentration of acetaldehyde due to the in-situ photo-deposition of Pt. However, whereas acetal formation is similar for Pt/anatase and Pt/rutile phase under air, under Ar, less acetal is generated on Pt/rutile in agreement with the production of more H₂.

Enabling alcohol as a hydrogen carrier using metal-organic framework-stabilized Ir-Sc bifunctional catalytic sites

Alcohols are attractive portable chemical carriers of hydrogen thanks to their reversible dehydrogenation, but the hydrogen release reaction is thermodynamically unfavorable. Coupling the alcohol dehydrogenation to acetal formation can shift the reaction thermodynamics for hydrogen production. Here, we stabilized Ir³⁺ and Sc³⁺ in a metal-organic framework (MOF) for tandem catalysis. The Ir³⁺ center bearing an α-hydroxybipyridine ligand catalyzes alcohol dehydrogenation, and the Sc³⁺ Lewis acid site catalyzes acetal formation that allows further dehydrogenation to form esters. The bifunctional UiO-bpyOH-IrCp-Sc catalyst effectively converts ethylene glycol to ester and H₂ without producing CO.

Selective Photocatalytic Activation of Ethanol C-H and O-H Bonds over Multi-Au@SiO2/TiO2: Role of Catalyst Surface Structure and Reaction Kinetics

The chemical bond diversity and flexible reactivity of biomass-derived ethanol make it a vital feedstock for the production of value-added chemicals but result in low conversion selectivity. Herein, composite catalysts comprising SiO₂-coated single- or multiparticle Au cores hybridized with TiO₂ nanoparticles (mono- or multi-Au@SiO₂/TiO₂, respectively) were fabricated via electrostatic self-assembly. The C-H and O-H bonds of ethanol were selectively activated (by SiO₂ and TiO₂, respectively) under irradiation to form CH₃CH^•(OH) or CH₃CH₂O^• radicals, respectively. The formation and depletion kinetics of these radicals was analyzed by electron spin resonance to reveal marked differences between mono- and multi-Au@SiO₂/TiO₂. Consequently, the selectivity of these catalysts for 1,1-diethoxyethane after 6 h irradiation was determined as 81 and 99%, respectively, which was attributed to the more pronounced effect of localized surface plasmon resonance for multi-Au@SiO₂/TiO₂. Notably, only acetaldehyde was formed on a Au/TiO₂ catalyst without a SiO₂ shell. Fourier transform infrared (FTIR) spectroscopy indicated that the C-H adsorption of ethanol was enhanced in the case of multi-Au@SiO₂/TiO₂, while NH₃ temperature-programmed desorption and pyridine adsorption FTIR spectroscopy revealed that multi-Au@SiO₂/TiO₂ exhibited enhanced surface acidity. Collectively, the results of experimental and theoretical analyses indicated that the adsorption of acetaldehyde on multi-Au@SiO₂/TiO₂ was stronger than that on Au/TiO₂, which resulted in the oxidative coupling of ethanol to afford 1,1-diethoxyethane on the former and the dehydrogenation of ethanol to acetaldehyde on the latter.

Upgrading of Ethanol to 1,1-Diethoxyethane by Proton-Exchange Membrane Electrolysis

The direct acetalization of ethanol is a significant challenge for upgrading bioethanol to value-added chemicals. In this study, 1,1-diethoxyethane (DEE) is selectively synthesized by the electrolysis of ethanol using a proton-exchange membrane (PEM) reactor. In the PEM reactor, a Pt/C catalyst promoted the electro-oxidation of ethanol to acetaldehyde. The Nafion membrane used as the PEM served as a solid acid catalyst for the acetalization of ethanol and electrochemically formed acetaldehyde. DEE was obtained at high faradaic efficiency (78 %) through sequential electrochemical and nonelectrochemical reactions. The DEE formation rate through PEM electrolysis was higher than that of reported systems. At the cathode, protons extracted from ethanol were reduced to H₂ . The electrochemical approach can be utilized as a sustainable process for upgrading bioethanol to chemicals because it can use renewable electricity and does not require chemical reagents (e. g., oxidants and electrolytes).

Selective Chloride-Mediated Neat Ethanol Oxidation to 1,1-Diethoxyethane via an Electrochemically Generated Ethyl Hypochlorite Intermediate

Selective primary alcohol oxidation to form aldehydes products without overoxidation to carboxylic acids remains a key chemistry challenge. Using simple alkylammonium chloride as the electrolyte with a glassy carbon working electrode in neat ethanol solvent, 1,1-diethoxyethane (DEE) was prepared with >95% faradaic efficiency (FE). DEE serves as a storage platform protecting acetaldehyde from overoxidation and volatilization. UV-vis spectroscopy shows that the reaction proceeds through an ethyl hypochlorite intermediate as the sole chloride oxidation product, and that this intermediate decomposes unimolecularly (rate constant k = (6.896 ± 0.516) × 10^-4 s^-1) to form HCl catalyst and acetaldehyde, which undergoes rapid nucleophilic attack by ethanol solvent to form the DEE product. This indirect oxidation mechanism enables ethanol oxidation at much less positive potentials due to the fast kinetics for chloride anion oxidation.

Photocatalytic degradation of MB by TiO2: studies on recycle and reuse of photocatalyst and treated water for seed germination

Photocatalysis is an effective way for treatment of wastewater and degradation of dyes. It is important to assess the reusability of photocatalyst and treated water after the treatment process. In this study, the photocatalytic activity of TiO₂ (titanium dioxide) and TiO₂-TMAOH (titanium dioxide-tetramethylammonium hydroxide) was analyzed for degradation of methylene blue dye. Enhanced degradation of methylene blue is observed while treated with TiO₂-TMAOH with photodegradation efficiency (PDE) 80% within 20 min. A further study shows the reusability of TiO₂ for degradation of dye for six cycles with a decrease in photodegradation efficiency from 90% (cycle-1) to 50% (cycle-2). Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and cyclic voltammetry (CV) analysis were carried out to identify the functional groups in treated water, traces of titanium, and TMAOH, respectively. Seed germination of Vigna radiata using TiO₂- and TiO₂-TMAOH-treated water shows equivalent and consistent growth. Water quality analysis of treated water shows improved biochemical oxygen demand (BOD) level (1.5 mg L^-1), which is suitable for reusability of water for many applications. The outcomes suggest treated water can be used for irrigation and plantation purposes.

Cooperative Coupling of Oxidative Organic Synthesis and Hydrogen Production over Semiconductor-Based Photocatalysts

Merging hydrogen (H₂) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H₂ fuel and high-value chemicals can be coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H₂ can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H₂ production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H₂ production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H₂ production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.

One Nanometer PtIr Nanowires as High-Efficiency Bifunctional Catalysts for Electrosynthesis of Ethanol into High Value-Added Multicarbon Compound Coupled with Hydrogen Production

The electrosynthesis of high-value-added multicarbon compounds coupled with hydrogen production is an efficient way to achieve carbon neutrality; however, the lack of effective bifunctional catalysts in electrosynthesis largely hinders its development. Herein, we report the first example on the highly efficient electrosynthesis of high-value-added 1,1-diethoxyethane (DEE) at the anode and high-purity hydrogen at the cathode using 1 nm PtIr nanowires (NWs) as the bifunctional catalysts. We demonstrate that the cell using 1 nm PtIr nanowires as the bifunctional catalysts can achieve a reported lowest voltage of 0.61 V to reach the current density of 10 mA cm^-2, much lower than those of the Pt NWs (0.85 V) and commercial Pt/C (0.86 V), and also can have the highest Faraday efficiencies of 85% for DEE production and 94.0% for hydrogen evolution in all the reported electrosynthesis catalysts. The in situ infrared spectroscopy study reveals that PtIr NWs can facilitate the activation of O-H and C-H bonds in ethanol, which is important for the formation of acetaldehyde intermediate, and finally DEE. In addition, the cell using PtIr NWs as bifunctional catalysts exhibits excellent stability by showing almost no obvious decrease in the Faraday efficiency of the DEE production.

Mechanistic insights into the acetate-accelerated synthesis of crystalline ceria nanoparticles

Lithium acetate was reported to accelerate the growth of crystalline ceria nanoparticles in ozone-mediated synthesis through promoting alcohol-like condensation reactions.

A TiO2 nanowire photocatalyst for dual-ion production in laser desorption/ionization (LDI) mass spectrometry

It has been challenging to detect small analytes in both positive and negative ion modes in MALDI-MS. Herein, TiO₂ nanowires are presented as a solid matrix to produce dual-ion of any analytes and to demonstrate the versatile applicability in LDI-MS.

Direct ethanol condensation to diethyl acetal in the vapour phase at atmospheric pressure over CuNP/SBA-15 catalysts

Of the biomass valorization technologies, bioethanol production and its selective conversion to diethyl acetal is of utmost importance to meet the increasing demand for bio-fuel additives.

Visible light-driven methanol dehydrogenation and conversion into 1,1-dimethoxymethane over a non-noble metal photocatalyst under acidic conditions

The dehydrogenation and conversion of methanol into 1,1-dimethoxymethane (DMM) was achieved over noble metal free photocatalyst CdS/Ni₂P under visible light.