Manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid medium: a kinetic and mechanistic study

The manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid has been studied spectrophotometrically at 25 °C and I = 1.60 mol dm⁻³. Stoichiometry analysis shows that one mole of glycerol reacts with two moles of cerium(IV) to give cerium(III) and glycolic aldehyde. The reaction is first order in both cerium(IV) and manganese(II), and the order with respect to glycerol concentration varies from first to zero order as the glycerol concentration increases. Increase in sulphuric acid concentration, added sulphate and bisulphate all decrease the rate. Added cerium(III) retards the rate of reaction, whereas glycolic aldehyde had no effect. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Mn(H₂O)₄]²⁺. A mechanism is proposed, and the reaction constants and activation parameters have been determined.     

Ruthenium‐Catalyzed Synthesis of Dialkoxymethane Ethers Utilizing Carbon Dioxide and Molecular Hydrogen

The synthesis of dimethoxymethane (DMM) by a multistep reaction of methanol with carbon dioxide and molecular hydrogen is reported. Using the molecular catalyst [Ru(triphos)(tmm)] in combination with the Lewis acid Al(OTf)₃ resulted in a versatile catalytic system for the synthesis of various dialkoxymethane ethers. This new catalytic reaction provides the first synthetic example for the selective conversion of carbon dioxide and hydrogen into a formaldehyde oxidation level, thus opening access to new molecular structures using this important C₁ source.     

Catalytic performance of acidic ionic liquid-functionalized silica in biodiesel production

Acidic ionic liquid ([BsAIm][OTf]) was immobilized on sulfhydryl-group-modified SiO₂ (MPS-SiO₂) via free radical addition reaction. The [BsAIm][OTf] loading on acidic ionic liquid-functionalized silica ([BsAIm][OTf]/SiO₂) was controlled through tuning the sulfydryl (SH) content of MPS-SiO₂. All the samples were characterized by FT-IR, elemental analysis, N₂ adsorption-desorption measurements and TG-DTA. The catalytic performance of [BsAIm][OTf]/SiO₂ in the esterification of oleic acid and the transesterification of glycerol trioleate for biodiesel production was investigated. The results showed that with the increase of [BsAIm][OTf] loading on SiO₂ the specific surface area and pore volume of [BsAIm][OTf]/SiO₂ decreased, and the pore diameter of [BsAIm][OTf]/SiO₂ narrowed. In the esterificaiton of oleic acid, the oleic acid conversion increased with the increasing [BsAIm][OTf] loading. In the transesterification of glycerol trioleate, with the increasing [BsAIm][OTf] loading the glycerol trioleate conversion decreased and the selectivities to glycerol monooleate and methyl oleate increased.     

Mesoporous silica-supported V-substituted heteropoly acid for efficient selective conversion of glycerol to formic acid

V-substituted polymolybdenum phosphoric acid (PV_xMo) supported on mesoporous silica was prepared and investigated as a catalyst for the oxidation of glycerol to formic acid in a batch operation. Different synthetic methods for PV_xMo supported on mesoporous silica were compared. Detailed characterizations of the final products were carried out by N₂ adsorption and desorption, XRD, HR-TEM, SEM, ICP-OES, XANES, NH₃-TPD, and FTIR to identify the chemical properties and the porous structure of silica-supported PV_xMo, as well as the strong interactions between PV_xMo with the silica skeleton. These critical properties explain the bifunctionality of silica-supported PV_xMo as a catalyst for the selective oxidation of glycerol to formic acid with standing stability.     

A novel and efficient method for inside selective esterification of terminal vic-diols

A novel and highly efficient procedure for inside selective esterification of terminal vic-diols has been achieved in one-pot via Yb(OTf)₃-catalyzed formation and partial hydrolysis of cyclic orthoesters. This method offers several advantages including wide compatibility with acid labile functional groups, and good to high regioselectivity and yields.     

Investigation of the catalytic activity of an electron-deficient vanadium(IV) tetraphenylporphyrin: A new, highly efficient and reusable catalyst for ring-opening of epoxides

In this work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], in the nucleophilic ring-opening of epoxides is reported. This new V(IV) catalyst was used as an efficient catalyst for alcoholysis with primary (methanol, ethanol and n-propanol), secondary (iso-propanol) and tertiary alcohols (tert-butanol), hydrolysis and acetolysis of epoxides with acetic acid and also for the conversion of epoxides to 1,2-diacetates with acetic anhydride, conversion of epoxides to thiiranes with ammonium thiocyanate and thiourea, and for conversion of epoxides to acetonides with acetone. The catalyst was reused several times without loss of its activity.     

Living polymerization of D,L‐3‐methylglycolide initiated with bimetallic (Al/Zn) μ‐oxo alkoxide and copolymers thereof

D,L ‐3‐Methylglycolide (MG) was successfully polymerized with bimetallic (Al/Zn) μ‐oxo alkoxide as an initiator in toluene at 90 °C. The effect of the initiator concentration and monomer conversion on the molecular weight was studied. It is shown that the polymerization of MG follows a living process. A kinetic study indicated that the polymerization approximates the first order in the monomer, and no induction period was observed. ¹H NMR spectroscopy showed that the ring‐opening polymerization proceeds through a coordination–insertion mechanism with selective cleavage of the acyl–oxygen bond of the monomer. On the basis of ¹H NMR and ¹³C NMR analyses, the selective cleavage of the acyl–oxygen bond of the monomer mainly occurs at the least hindered carbonyl groups (P₁ = 0.84, P₂ = 0.16). Therefore, the main chain of poly(D,L ‐lactic acid‐co‐glycolic acid) (50/50 molar ratio) obtained from the homopolymerization of MG was primarily composed of alternating lactyl and glycolyl units. The diblock copolymers poly(ϵ‐caprolactone)‐b‐poly(D,L ‐lactic acid‐alt‐glycolic acid) and poly(L ‐lactide)‐b‐poly(D,L ‐lactic acid‐alt‐glycolic acid) were successfully synthesized by the sequential living polymerization of related lactones (ϵ‐caprolactone or L ‐lactide). ¹³C NMR spectra of diblock copolymers clearly show their pure diblock structures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 357–367, 2001     

负载型纳米Au/Cr_2O_3催化甘油氧化合成甘油酸

制备了一系列负载型纳米Au/Cr_2O_3催化剂,采用ICP、FTIR、XRD和N2吸附脱附对所制备的催化剂进行了表征.以3%的H_2O_2为氧化剂,考察其对甘油选择性氧化反应的催化性能.结果表明,该类催化剂在甘油选择性氧化反应中表现出了较好的催化性能,其中Au/Cr_2O_3(0.95%)的催化性能最好,甘油转化率可达81.5%,甘油酸选择性为67.0%,且该非均相催化剂重复使用10次后仍保持较高的催化活性.     

Lewis Acid Coupled Electron Transfer of Metal–Oxygen Intermediates

Redox‐inactive metal ions and Brønsted acids that function as Lewis acids play pivotal roles in modulating the redox reactivity of metal–oxygen intermediates, such as metal–oxo and metal–peroxo complexes. The mechanisms of the oxidative C?H bond cleavage of toluene derivatives, sulfoxidation of thioanisole derivatives, and epoxidation of styrene derivatives by mononuclear nonheme iron(IV)–oxo complexes in the presence of triflic acid (HOTf) and Sc(OTf)₃ have been unified as rate‐determining electron transfer coupled with binding of Lewis acids (HOTf and Sc(OTf)₃) by iron(III)–oxo complexes. All logarithms of the observed second‐order rate constants of Lewis acid‐promoted oxidative C?H bond cleavage, sulfoxidation, and epoxidation reactions of iron(IV)–oxo complexes exhibit remarkably unified correlations with the driving forces of proton‐coupled electron transfer (PCET) and metal ion‐coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes were taken into account. The binding of HOTf and Sc(OTf)₃ to the metal–oxo moiety has been confirmed for Mn^IV–oxo complexes. The enhancement of the electron‐transfer reactivity of metal–oxo complexes by binding of Lewis acids increases with increasing the Lewis acidity of redox‐inactive metal ions. Metal ions can also bind to mononuclear nonheme iron(III)–peroxo complexes, resulting in acceleration of the electron‐transfer reduction but deceleration of the electron‐transfer oxidation. Such a control on the reactivity of metal–oxygen intermediates by binding of Lewis acids provides valuable insight into the role of Ca²⁺ in the oxidation of water to dioxygen by the oxygen‐evolving complex in photosystem II.     

Chemical oxidative polymerization of m-phenylenediamine and its derivatives using aluminium triflate as a co-catalyst

Aromatic diamine monomers, including m-phenylenediamine (mPD), 2-methyl-m-phenylenediamine (2Me-mPD), 4-methyl-m-phenylenediamine (4Me-mPD) and trimethyl-m-phenylenediamine (tMe-mPD), were polymerized by chemical oxidation using ammonium persulfate as an oxidant. Aluminium triflate (Al(OTf)₃) was also used for the first time as a co-catalyst under various polymerization conditions. The polymerization yield was improved when Al(OTf)₃ was introduced to the polymerization reaction for most polymers. The poly(2-methyl-m-phenylenediamine) (P(2Me-mPD)), poly(4-methyl-m-phenylenediamine) (P(4Me-mPD)) and poly(trimethyl-m-phenylenediamine) (P(tMe-mPD)) polymers exhibited better solubility than poly(m-phenylenediamine) (P(mPD)) polymers in most common solvents. The homopolymers obtained were characterized by FT-IR, ¹H and ¹³C NMR, WAXD and TGA. The results showed that the yield, solubility and structure of the polymers are significantly dependent on the polymerization conditions. TGA measurements indicated that the polymers have good thermal stability and decompose above 400 °C in nitrogen.     

Simultaneous co-Photocatalytic CO2 Reduction and Ethanol Oxidation towards Synergistic Acetaldehyde Synthesis

Photocatalytic conversion of CO₂ is of great interest but it often suffers sluggish oxidation half reaction and undesired by-products. Here, we report for the first the simultaneous co-photocatalytic CO₂ reduction and ethanol oxidation towards one identical value-added CH₃CHO product on a rubidium and potassium co-modified carbon nitride (CN-KRb). The CN-KRb offers a record photocatalytic activity of 1212.3 μmol h⁻¹g⁻¹ with a high selectivity of 93.3 % for CH₃CHO production, outperforming all the state-of-art CO₂ photocatalysts. It is disclosed that the introduced Rb boosts the *OHCCHO fromation and facilitates the CH₃CHO desorption, while K promotes ethanol adsorption and activation. Moreover, the H⁺ stemming from ethanol oxidation is confirmed to participate in the CO₂ reduction process, endowing near ideal overall atomic economy. This work provides a new strategy for effective use of the photoexcited electron and hole for high selective and sustainable conversion of CO₂ paired with oxidation reaction into identical product.     

多相固体催化剂用于甘油氧化制乳酸研究进展

随着新的全球气候协议下的中国双碳行动计划的实施, 开发和利用可再生生物质资源显得极为重要. 甘油作为生物柴油在生产过程中的主要副产物, 将其催化转化成各种高附加值衍生物受到广泛关注, 其中甘油选择性氧化为乳酸具有巨大的应用前景. 近年来, 采用固体催化剂催化氧化甘油制乳酸成为国内外学者研究的热点. 我们综述了固体催化剂用于甘油催化转化制备乳酸的研究现状, 对甘油催化转化为乳酸的反应途径做了分析, 并讨论了影响催化剂活性的因素, 对当前所存在的问题提出建议, 也对未来相关催化剂制备发展进行了展望.     

Nitrogen-doped Co3O4 nanowires enable high-efficiency electrochemical oxidation of 5-hydroxymethylfurfural

Developing highly efficient and cost-effective catalysts for electrochemically oxidizing biomass-derived 5-hydroxymethylfurfural（HMF） into value-added 2,5-furandicarboxylic acid（FDCA） is of great importance.Herein, we report a controllable nitrogen doping strategy to significantly improve the catalytic activity of Co₃O₄ nanowires for highly selective electro-oxidation of HMF into FDCA. The nitrogen doping leads to the generation of defects including nitrogen dopants and oxy...     

An Effective Pd–Ni2P/C Anode Catalyst for Direct Formic Acid Fuel Cells

The direct formic acid fuel cell is an emerging energy conversion device for which palladium is considered as the state‐of‐the‐art anode catalyst. In this communication, we show that the activity and stability of palladium for formic acid oxidation can be significantly enhanced using nickel phosphide (Ni₂P) nanoparticles as a cocatalyst. X‐ray photoelectron spectroscopy (XPS) reveals a strong electronic interaction between Ni₂P and Pd. A direct formic acid fuel cell incorporating the best Pd–Ni₂P anode catalyst exhibits a power density of 550 mW cm^?2, which is 3.5 times of that of an analogous device using a commercial Pd anode catalyst.     

Accelerating H2 Evolution by Anodic Semi-dehydrogenation of Tetrahydroisoquinolines in Water over Co3O4 Nanoribbon Arrays Decorated Nickel Foam

Coupling the H₂ evolution reaction in water with thermodynamically favorable organic oxidation reactions is highly desirable, because it can enhance the energy conversion efficiency compared with electrocatalytic water splitting, and produce value-added chemicals instead of O₂ in the anodic reaction. Herein, Co₃O₄ nanoribbon arrays in situ grown on nickel foam (Co₃O₄@NF) was employed as an effective electrocatalyst for the selective oxidation of tetrahydroisoquinolines (THIQs). Various value-added semi-dehydrogenation products including dihydroisoquinolines with electro-deficient or -rich groups could be obtained with moderate yields and faradaic efficiencies. Benefitting from the rich surface active sites of Co₃O₄@NF, a two-electrode (Co₃O₄@NF||Pt) electrolytic system drove a benchmark current density of 10 mA cm⁻² at a cell voltage as low as 1.446 V in 1.0 M KOH aqueous solution containing 0.02 M THIQ, which was reduced by 174 mV in comparison with that of overall water splitting.     

Mechanistic studies of oxidation of maltose and lactose by [H2OBr]+ in presence of chloro-complex of Rh(III) as homogeneous catalyst

Kinetic studies in homogeneously Rh(III)-catalyzed oxidation of reducing sugars, i.e. maltose and lactose, by N-bromoacetamide (NBA) in the presence of perchloric acid have been made at 40 °C using mercuric acetate as Br⁻ ion scavenger. The results obtained for the oxidation of both reducing sugars show first-order dependence of the reactions on NBA at its low concentrations, which shifts towards zero-order at its higher concentrations. First-order kinetics in [Rh(III)] and zero-order kinetics in [reducing sugar] were observed. Positive effect of [Cl⁻] was observed in the oxidation of both maltose and lactose. Order of reaction was found to be one and half (1.5) throughout the variation of [H⁺] in the oxidation of both maltose and lactose. An increase in the rate of reaction with the decrease in [Hg(OAc)₂] and [NHA] was observed for both the redox systems. The rate of oxidation is unaffected by the change in ionic strength (μ) of the medium. The main oxidation products of the reactions were identified as formic acid and arabinonic acid in the case of maltose and formic acid, arabinonic acid and lyxonic acid in the case of lactose. A common mechanism for the oxidation of both maltose and lactose, showing the formation of most reactive activated complex, [RhCl₄(H₃O)H₂OBr]⁺, and an unreactive complex, [RhCl₄(H₂O)(H₂OBrHg)]²⁺, has been proposed. Various activation parameters have also been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.     

Computational Study of Formic Acid Dehydrogenation Catalyzed by AlIII–Bis(imino)pyridine

The mechanism of formic acid dehydrogenation catalyzed by the bis(imino)pyridine‐ligated aluminum hydride complex (PDI^2?)Al(THF)H (PDI=bis(imino)pyridine) was studied by density functional theory calculations. The overall transformation is composed of two stages: catalyst activation and the catalytic cycle. The catalyst activation begins with O?H bond cleavage of HCOOH promoted by aluminum–ligand cooperation, followed by HCOOH‐assisted Al?H bond cleavage, and protonation of the imine carbon atom of the bis(imino)pyridine ligand. The resultant doubly protonated complex (^H,HPDI)Al(OOCH)₃ is the active catalyst for formic acid dehydrogenation. Given this, the catalytic cycle includes β‐hydride elimination of (^H,HPDI)Al(OOCH)₃ to produce CO₂, and the formed (^H,HPDI)Al(OOCH)₂H mediates HCOOH to release H₂.     

Stereocontrol during photo-initiated controlled/living radical polymerization of acrylamide in the presence of Lewis acids

Poly(acrylamide) (PAM) with controlled molecular weight and tacticity was prepared by UV-irradiation-initiated controlled/living radical polymerization in the presence of dibenzyl trithiocarbonate (DBTTC) and Y(OTf)₃. The rapid and facile photo-initiated controlled/living polymerization at ambient temperature led to controlled molecular weight and narrow polydispersity (M_w/M_n = 1.12-1.24) of PAM. The coordination of Y(OTf)₃ with the last two amide groups in the growing chain radical effectively enhanced isotacticity of PAM. The isotactic sequence of dyads (m), triads (mm) and pentads (mmmm) in PAM were 70.32%, 50.95%, and 29.97%, respectively, which were determined by the resonance of methine (CH) groups in PAM under ¹³C NMR experiment. Factors affecting stereocontrol during the polymerization were studied, including the type of Lewis acids, concentration of Y(OTf)₃, and monomer conversion. It is intriguing that the meso tacticity increased gradually with chain propagation and quite higher isotacticity (m = 93.01%, mm = 86.57%) was obtained in the later polymerization stage (conversion 65-85%).     

Slow Reactant–Water Exchange and High Catalytic Performance of Water‐Tolerant Lewis Acids

³¹P nuclear magnetic resonance (NMR) spectroscopic measurement with trimethylphosphine oxide (TMPO) was applied to evaluate the Lewis acid catalysis of various metal triflates in water. The original ³¹P NMR chemical shift and line width of TMPO is changed by the direct interaction of TMPO molecules with the Lewis acid sites of metal triflates. [Sc(OTf)₃] and [In(OTf)₃] had larger changes in ³¹P chemical shift and line width by formation of the Lewis acid–TMPO complex than other metal triflates. It originates from the strong interaction between the Lewis acid and TMPO, which results in higher stability of [Sc(OTf)₃TMPO] and [In(OTf)₃TMPO] complexes than other metal triflate–TMPO complexes. The catalytic activities of [Sc(OTf)₃] and [In(OTf)₃] for Lewis acid‐catalyzed reactions with carbonyl compounds in water were far superior to the other metal triflates, which indicates that the high stability of metal triflate–carbonyl compound complexes cause high catalytic performance for these reactions. Density functional theory (DFT) calculation suggests that low LUMO levels of [Sc(OTf)₃] and [In(OTf)₃] would be responsible for the formation of stable coordination intermediate with nucleophilic reactant in water.     

Photocatalytic hydrogen generation using glycerol wastewater over Pt/TiO2

Using glycerol as electron donor, photocatalytic hydrogen generation over Pt/TiO₂ was investigated. The results show that glycerol can not only improve the efficiency of photocatalytic hydrogen generation but can also be decomposed effectively. The factors which affect photocatalytic hydrogen generation, such as irradiation time, initial concentration of the glycerol solution, pH-value of the suspensions and the coexisting substances were studied. The final oxidation products of glycerol were H₂O and CO₂. Glyceraldhyde, glycoladehyde, glycolic acid and formaldehyde were identified as the intermediates. A possible reaction mechanism was discussed. __________ Translated from Journal of Molecular Catalysis, 2008, 22(2) (in Chinese)