Über die durch Riesencluster des Palladiums katalysierte Oxydation von Ameisensäure

Oxidation of Formic Acid Catalyzed by Giant Palladium Clusters Liquid-phase oxidation of formic acid by oxygen in acetonitrile solutions is catalyzed by giant clusters Pd₅₆₁Phen₆₀(OAc)₁₈₀ or Pd₅₆₁Phen₆₀(O)₆₀ at 20–70°C. The reaction is first-order in the cluster and formic acid concentrations. Dependence of the reaction rates on O₂ concentration is described by Michaelis-type equation. Kinetic isotope effects are found to be k(HCOOH)/k(HCOOD) = 1.1 ± 0.1 and k(HCOOH)/k(DCOOD) = 1.0 ± 0.1. On the base of the kinetic data the reaction mechanism is discussed.     

Ozone-Assisted Catalysis of Toluene with Layered ZSM-5 and Ag/ZSM-5 Zeolites

This paper presents a new type of ozone-assisted catalysis for toluene decomposition. The different catalytic activities of ZSM-5 and Ag/ZSM-5 were incorporated into a layered catalyst with a tandem configuration. Instead of increasing the amount of metal catalyst, the layered catalyst was formed, which had an equal amount of bare ZSM-5 and Ag/ZSM-5 and could achieve both high toluene conversion and CO₂ selectivity concurrently. The properties of each catalyst were evaluated with respect to toluene conversion, formation of intermediates, CO₂ selectivity and ozone demand factor. The bare ZSM-5 exhibited higher toluene conversion than the Ag/ZSM-5, while its activity toward deep oxidation was limited. However, the Ag/ZSM-5 was found to be effective for the deep oxidation of reaction intermediates (HCOOH and CO). Separate oxidation tests with HCOOH and CO revealed that the ZSM-5-supported Ag nanoparticles could oxidize the HCOOH and CO in the absence of ozone, which was not possible with the bare ZSM-5. Plausible pathways for the oxidation of toluene with O₃ over ZSM-5 and Ag/ZSM-5 were proposed based on the experimental evidence.     

Plasmonic Titanium Nitride Tubes Decorated with Ru Nanoparticles as Photo-Thermal Catalyst for CO2 Methanation

Photo-thermal catalysis has recently emerged as a viable strategy to produce solar fuels or chemicals using sunlight. In particular, nanostructures featuring localized surface plasmon resonance (LSPR) hold great promise as photo-thermal catalysts given their ability to convert light into heat. In this regard, traditional plasmonic materials include gold (Au) or silver (Ag), but in the last years, transition metal nitrides have been proposed as a cost-efficient alternative. Herein, we demonstrate that titanium nitride (TiN) tubes derived from the nitridation of TiO₂ precursor display excellent light absorption properties thanks to their intense LSPR band in the visible–IR regions. Upon deposition of Ru nanoparticles (NPs), Ru-TiN tubes exhibit high activity towards the photo-thermal CO₂ reduction reaction, achieving remarkable methane (CH₄) production rates up to 1200 mmol g⁻¹ h⁻¹. Mechanistic studies suggest that the reaction pathway is dominated by thermal effects thanks to the effective light-to-heat conversion of Ru-TiN tubes. This work will serve as a basis for future research on new plasmonic structures for photo-thermal applications in catalysis.     

Pd2+-Initiated Formic Acid Decomposition: Plausible Pathways for C-H Activation of Formate

Formic acid (HCOOH, FA) has long been considered as a promising hydrogen-storage material due to its efficient hydrogen release under mild conditions. In this work, FA decomposes to generate CO₂ and H₂ selectively in the presence of aqueous Pd²⁺ complex solutions at 333 K. Pd(NO₃)₂ was the most effective in generating H₂ among various Pd²⁺ complexes explored. Pd²⁺ complexes were in situ reduced to Pd⁰ species by the mixture of FA and sodium formate (SF) during the course of the reaction. Since C−H activation reaction of Pd²⁺-bound formate is occurred for both Pd²⁺ reduction and H₂/CO₂ gas generation, FA decomposition pathways using several Pd²⁺ species were explored using density functional theory (DFT) calculations. Rotation of formate bound to Pd²⁺, β-hydride elimination, and subsequent CO₂ and H₂ elimination by formic acid were examined, providing different energies for rate determining step depending on the ligand electronics and geometries coordinated to the Pd²⁺ complexes. Finally, Pd²⁺ reduction toward Pd⁰ pathways were explored computationally either by generated H₂ or reductive elimination of CO₂ and H₂ gas.     

Radiation Chemistry of Polysaccharides: 1. Mechanisms of Carbon Monoxide and Formic Acid Formation

Based on an analysis of author's experimental results and published data on the buildup of HCOOH and CO in starches and other high polymers of glucose irradiated in the presence of O₂, it was concluded that both of these products result from multistage transformations of a primary radical of H abstraction from C1. Peroxide radicals are the source of HCOOH, whereas acyl radicals, which are produced in radical reactions with aldehyde groups, are the precursor of CO. Based on the values of G(HCOOH), G(CO), and G(cleavage) and the mass balance on these products, a conclusion was drawn that the formation of these products requires the degradation of three neighboring monomer units. A reaction mechanism for the formation of HCOOH and CO was proposed.     

Synthesis of large palladium clusters. The preparation of Pd38(CO)28(PR3)12 (R = Et,Bun) and Pd34(CO)24(PEt3)12

Several methods for the synthesis of the Pd₃₈(CO)₂₈L₁₂ cluster (L = PEt₃) by treatment of Pd₁₀(CO)₁₂L₆ with CF₃COOH-Me₃NO, CF₃COOH-H₂O₂, Pd(OAc)₂-Me₃NO, and Pd₂(dba)₃ mixtures (dba is dibenzylideneacetone) were proposed. The tri-n-butylphosphine analog, Pd₃₈(CO)₂₈(PBu₃)₁₂, was synthesized by the reaction of Pd₁₀(CO)₁₄(PBu₃)₄ with Me₃NO. The reaction of Pd₄(CO)₅L₄ with Pd₂(dba)₃ yields clusters with an icosahedral packing of the metal atoms, Pd₃₄(CO)₂₄L₁₂ and Pd₁₆(CO)₁₃L₉.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 167–170, January, 1995.     

Photo–thermo Catalytic Oxidation over a TiO2-WO3-Supported Platinum Catalyst

Photo–thermo catalysis, which integrates photocatalysis on semiconductors with thermocatalysis on supported nonplasmonic metals, has emerged as an attractive approach to improve catalytic performance. However, an understanding of the mechanisms in operation is missing from both the thermo- and photocatalytic perspectives. Deep insights into photo–thermo catalysis are achieved via the catalytic oxidation of propane (C₃H₈) over a Pt/TiO₂-WO₃ catalyst that severely suffers from oxygen poisoning at high O₂/C₃H₈ ratios. After introducing UV/Vis light, the reaction temperature required to achieve 70 % conversion of C₃H₈ lowers to a record-breaking 90 °C from 324 °C and the apparent activation energy drops from 130 kJ mol⁻¹ to 11 kJ mol⁻¹. Furthermore, the reaction order of O₂ is −1.4 in dark but reverses to 0.1 under light, thereby suppressing oxygen poisoning of the Pt catalyst. An underlying mechanism is proposed based on direct evidence of the in-situ-captured reaction intermediates.     

Influence of H3PMo12O40/SiO2 thermal treatment on adsorbed forms of formaldehyde and formic acid

Effect of the H₃PMo₁₂O₄₀/SiO₂(P-Mo-HPA) thermal treatment on adsorbed forms of HCOOH and H₂CO has been studied by IR spectroscopy. On the sample pretreated at 150°C, HCOOH adsorbed mainly as hydrogen-bonded complexes. The HPA calcination at 350°C resulted in the formation of surface formates along with hydrogen-bonded complexes. This proves the formation of coordinatively unsaturated surface cations (Lewis acid sites) during HPA dehydration. Alteration of the surface composition due to dehydration was found to have a major influence on the H₂CO adsorbed forms.     

Mechanism of the chain process forming H2 in the photooxidation of formaldehyde

A mechanism for the formation in a chain of H₂, CO, and HCOOH in the photooxidation of formaldehyde is proposed. This mechanism is initiated by the addition of HO₂ to formaldehyde. Hydrogen atoms are produced by the thermal dissociation of the HOCH₂O radical: HOCH₂O → H + HCOOH; ΔH = + 3.2 kcal/mol [5]. Photolysis of CH₂O? O₂? NO mixtures and product analysis were carried out in conjunction with kinetic simulation yielding an estimate for the activation energy of the dissociation reaction : E₅ = 14.9 ± 1.0 kcal/mol. Previous observations of this chain process are considered in view of this mechanism.     

Energy Transfer Dynamics of Formate Decomposition on Cu(110)

Energy transfer dynamics of formate (HCOO_a) decomposition on a Cu(110) surface has been studied by measuring the angle‐resolved intensity and translational energy distributions of CO₂ emitted from the surface in a steady‐state reaction of HCOOH and O₂. The angular distribution of CO₂ shows a sharp collimation with the direction perpendicular to the surface, as represented by cosⁿ θ (n= 6). The mean translational energy of CO₂ is measured to be as low as 100 meV and is independent of the surface temperature (T _s). These results clearly indicate that the decomposition of formate is a thermal non‐equilibrium process in which a large amount of energy released by the decomposition reaction of formate is transformed into the internal energies of CO₂ molecules. The thermal non‐equilibrium features observed in the dynamics of formate decomposition support the proposed Eley–Rideal (ER)‐type mechanism for formate synthesis on copper catalysts.     

Carbonylation of nitrobenzene in methanol with palladium bidentate phosphane complexes: an unexpectedly complex network of catalytic reactions, centred around a Pd-imido intermediate

The reactivity of palladium complexes of bidentate diaryl phosphane ligands (P₂) was studied in the reaction of nitrobenzene with CO in methanol. Careful analysis of the reaction mixtures revealed that, besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MPC), N,N′‐diphenylurea (DPU), aniline, azobenzene (Azo) and azoxybenzene (Azoxy)], large quantities of oxidation products of methanol were co‐produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H₂O, and CO). From these observations, it is concluded that several catalytic processes operate simultaneously, and are coupled via common catalytic intermediates. Starting from a P₂Pd⁰ compound formed in situ, oxidation to a palladium imido compound P₂Pd^II?NPh, can be achieved by de‐oxygenation of nitrobenzene 1) with two molecules of CO, 2) with two molecules of CO and the acidic protons of two methanol molecules, or 3) with all four hydrogen atoms of one methanol molecule. Reduction of P₂Pd^II?NPh to P₂Pd⁰ makes the overall process catalytic, while at the same time forming Azo(xy), MPC, DPU and aniline. It is proposed that the Pd–imido species is the central key intermediate that can link together all reduction products of nitrobenzene and all oxidation products of methanol in one unified mechanistic scheme. The relative occurrence of the various catalytic processes is shown to be dependent on the characteristics of the catalysts, as imposed by the ligand structure.     

Formic acid catalyzed gas-phase reaction of H2O with SO3 and the reverse reaction: a theoretical study

The formic acid catalyzed gas‐phase reaction between H₂O and SO₃ and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc‐pv(T+d)z and CCSD(T)//MP2/aug‐cc‐pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H₂O with SO₃ is lowered through formic acid catalysis from 15.97 kcal mol^?1 to ?15.12 and ?14.83 kcal mol^?1 for the formed H₂O ??? SO₃ complex plus HCOOH and the formed H₂O ??? HCOOH complex plus SO₃, respectively, at the CCSD(T)//MP2/aug‐cc‐pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to ?3.07 kcal mol^?1 from 35.82 kcal mol^?1 with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO₃+H₂O reaction with formic acid is 10⁵ times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H₂SO₄ reaction is about 10^?13 cm³ molecule^?1 s^?1 in the temperature range 200–280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO₃ and H₂SO₄ in atmospheric chemistry.     

Synthesis of big palladium clusters. Preparation of Pd23(CO)20(PEt3)8

Selective methods for the synthesis of the cluster Pd₂₃(CO)₂₀L₈, L=PEt₃, have been suggested. The compound has been prepared by two routes: by the reaction of Pd₁₀(CO)₁₂L₆ with Me₃NO in the presence of HOAc with removal of CO from the gas phase, and by the reaction of Pd₁₀(CO)₁₂L₆ with Pd(OAc)₂ and CO followed by oxidation by Me₃NO in an inert atmosphere.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1299–1300, July, 1993.     

Pd-Cu-Clx/Al2O3催化剂对CO氧化的稳定性

CO催化氧化广泛应用于空气净化、机动车尾气治理和CO气体传感器中.在CO氧化催化剂设计与制备过程中,催化剂与使用环境密切相关.例如工业和机动车尾气净化需要在高温(200–600°C)下进行,而对于半密闭空间(隧道或者地下停车场)空气净化需要在室温和高相对湿度下进行.频繁冷启动导致半密闭空间CO浓度累积而超过排放控制标准,因此制备室温、高相对湿度下CO氧化催化剂是面临的重要问题之一.负载型Wacker催化剂对于CO低温催化氧化的研究一直受到广泛关注.环境中少量水的存在会促进负载型Wacker催化剂对CO的低温氧化性能,但随着水沉积量的增加,活性位点将被覆盖,并且Pd和Cu活性组分之间的紧密结构被破坏,从而导致催化剂的失活,即催化剂的稳定性变差.因此,为了提高催化剂在高相对湿度下的稳定性,利用二乙氧基二甲基硅烷对Al2O3载体进行硅烷化处理,以增加载体的疏水性,考察载体疏水改性对CO低温氧化过程中催化剂稳定性的影响.催化剂的稳定性测试结果表明,在0°C,100%相对湿度条件下,未改性催化剂在约20 h内CO转化率由81%下降到50%;载体硅烷化后制备的催化剂在反应进行150 h后,CO转化率仍保持在78%,即反应活性未见降低.由此表明催化剂载体经有机硅烷改性后,可显著增强催化剂在低温、高相对湿度下的稳定性.N2吸附/脱附和水吸附实验结果表明,载体硅烷化改性并未对催化剂的比表面积产生影响,但显著降低了催化剂上水沉积速度和沉积量,未改性催化剂的初始吸水速度是改性后催化剂的4倍,但改性后催化剂的饱和吸水率仅占未改性催化剂的1/3.X射线衍射结果表明,载体预处理后活性物种Cu2(OH)3Cl晶粒尺寸有所增加.氢气程序升温还原、X射线光电子能谱结果表明,载体硅烷化预处理改善了催化剂中Cu和Pd物种的化学分布及接触状态,增加了与Pd物种紧密接触的Cu物种的量,从而促进了Cu物种的还原.与此同时,载体硅烷化显著降低了催化剂表面Cl离子的浓度,从而影响到对CO吸附.为了进一步研究水与催化剂稳定性之间的关系,采用原位红外漫反射(In situ DRIFT)对催化剂进行表征.负载型Wacker催化剂对CO氧化反应机理为:Pd是CO氧化反应的活性中心,通过Pd和Cu物种之间的氧化还原循环来实现CO氧化,且Pd+比Pd2+具有更高的CO氧化性能.反应气氛中水的存在,有利于CO在Pd+上氧化、以及金属态Pd被Cu2+物种再氧化的过程,同时水也显著促进了催化剂表面碳酸盐的生成以及抑制了活性物种Pd+生成.与表面碳酸盐累积相比,水对于活性物种Pd+生成的抑制作用是导致催化剂活性降低的主要原因.     

金属簇合物[(n-Bu)4N]3[WS4Ag3X3Br](X=Cl,Br,I)的热行为和热分解反应动力学

用TG-DTG-DTA联用技术研究了金属簇合物[(n-Bu)₄N]₃[WS₄Ag₃X₃Br](X=Cl,Br,I)在动态氮气气氛中的热行为和热性质,通过对热分解过程中各步反应中间体的元素分析跟踪,判断了相应的分解组分;并结合其物质结构进行了讨论。对各步反应进行了动力学分析,并通过活化能和反应进程的依赖关系探讨了反应的复杂性。     

Photo–thermo Catalytic Oxidation over a TiO2‐WO3‐Supported Platinum Catalyst

Photo–thermo catalysis, which integrates photocatalysis on semiconductors with thermocatalysis on supported nonplasmonic metals, has emerged as an attractive approach to improve catalytic performance. However, an understanding of the mechanisms in operation is missing from both the thermo‐ and photocatalytic perspectives. Deep insights into photo–thermo catalysis are achieved via the catalytic oxidation of propane (C₃H₈) over a Pt/TiO₂‐WO₃ catalyst that severely suffers from oxygen poisoning at high O₂/C₃H₈ ratios. After introducing UV/Vis light, the reaction temperature required to achieve 70 % conversion of C₃H₈ lowers to a record‐breaking 90 °C from 324 °C and the apparent activation energy drops from 130 kJ mol^?1 to 11 kJ mol^?1. Furthermore, the reaction order of O₂ is ?1.4 in dark but reverses to 0.1 under light, thereby suppressing oxygen poisoning of the Pt catalyst. An underlying mechanism is proposed based on direct evidence of the in‐situ‐captured reaction intermediates.     

Sonolysis of formic acid-water mixtures

Mixtures of formic acid and water were insonated with 300 kHz ultrasonic waves under an atmosphere of argon. H₂, CO₂, CO and very small amounts of oxalic acid are the products. The oxalic acid yield decreases with increasing HCOOH concentration. However, the yields of the other products pass through a maximum at 15 M. A mechanism is discussed where the decomposition of HCOOH into radicals plays only a minor role, the main reactions being thermal dehydration. The reactions are attributed to the high temperatures which exist in the adiabatic compression phase of cavitating argon bubbles, the temperature becoming lower with increasing HCOOH content of the gas bubbles.     

PPh3/I2/HCOOH: An efficient CO source for the synthesis of phthalimides

A straightforward and general method has been developed for the synthesis of phthalimide derivatives from 2-iodobenzamides and PPh₃/I₂/HCOOH in the presence of a catalytic amount of Pd(OAc)₂. The reaction results demonstrate that PPh₃/I₂/HCOOH is a facile, efficient and safe CO source. The whole process is carried out in toluene at 80?°C and furnishes the desired products in good to excellent yields.     

PdCl2-CuCl2/Al2O3催化剂低温催化CO氧化的失活机理

采用X射线衍射、N₂吸-脱附、X射线光电子能谱分析、氢气-程序升温还原和原位红外漫反射等方法对新鲜和失活的PdCl₂-CuCl₂/Al₂O₃低温催化CO氧化催化剂进行表征,研究了高相对湿度(100%)下催化剂的失活机理.结果表明,催化剂表面沉积的水使得活性铜物种容易从催化剂表面向载体孔道内部迁移,由于Pd、Cu相互作用弱化从而减弱了Pd与Cu物种间的相互作用,使得催化剂的氧化还原性能受到影响,抑制了Pd⁰再氧化为Pd²⁺的过程,从而因CO氧化反应中催化剂氧化还原循环受阻而导致失活.     

Solar‐Driven Water–Gas Shift Reaction over CuOx/Al2O3 with 1.1 % of Light‐to‐Energy Storage

Hydrogen production from coal gasification provides a cleaning approach to convert coal resource into chemical energy, but the key procedures of coal gasification and thermal catalytic water–gas shift (WGS) reaction in this energy technology still suffer from high energy cost. We herein propose adopting a solar–driven WGS process instead of traditional thermal catalysis, with the aim of greatly decreasing the energy consumption. Under light irradiation, the CuO_x/Al₂O₃ delivers excellent catalytic activity (122 μmol g_cat^?1 s^?1 of H₂ evolution and >95 % of CO conversion) which is even more efficient than noble‐metal‐based catalysts (Au/Al₂O₃ and Pt/Al₂O₃). Importantly, this solar‐driven WGS process costs no electric/thermal power but attains 1.1 % of light‐to‐energy storage. The attractive performance of the solar‐driven WGS reaction over CuO_x/Al₂O₃ can be attributed to the combined photothermocatalysis and photocatalysis.