Catalytic properties of palygorskite supported Ru and Pd for efficient oxidation of alcohols

Natural palygorskite (PG) was employed to prepare cost-effective, reusable supported catalyst of Pd/PG and Ru/PG through wet impregnation method. The catalysts were characterized through AFM, ICP-AES, XPS, XRD, BET, TEM and FTIR. The catalytic properties of the synthesized catalysts were assessed and optimized through oxidation of alcohols with PhIO as oxidant. It showed that the existence of Ru and Pd in the catalysts dramatically enhanced the catalytic activity with a prominent selectivity of far more than 99% compared with the palygorskite.     

甲苯液相选择氧化反应催化剂研究进展

以过渡金属氧化物及其负载型催化剂、杂多酸及其负载型催化剂、过渡金属络合物及其负载型催化剂、沸石分子筛基催化剂、超临界CO2介质催化反应体系为线索,评述了各类甲苯液相选择氧化反应催化剂的特性和近年来的研究进展,展望了甲苯液相选择氧化反应催化剂的发展方向,提出以反应对催化剂的结构和性质为指导来研制高效、绿色的催化剂仍是甲苯液相选择氧化反应的关键。     

Preparation of recoverable Ru catalysts for liquid-phase oxidation and hydrogenation reactions

We here report the synthesis, characterization and catalytic performance of new supported Ru(III) and Ru(0) catalysts. In contrast to most supported catalysts, these new developed catalysts for oxidation and hydrogenation reactions were prepared using nearly the same synthetic strategy, and are easily recovered by magnetic separation from liquid phase reactions. The catalysts were found to be active in both forms, Ru(III) and Ru(0), for selective oxidation of alcohols and hydrogenation of olefins, respectively. The catalysts operate under mild conditions to activate molecular oxygen or molecular hydrogen to perform clean conversion of selected substrates. Aryl and alkyl alcohols were converted to aldehydes under mild conditions, with negligible metal leaching. If the metal is properly reduced, Ru(0) nanoparticles immobilized on the magnetic support surface are obtained, and the catalyst becomes active for hydrogenation reactions.     

Novel dicopper(II)-tetracarboxylates as catalysts for selective oxidation of benzyl alcohols with aqueous TBHP

A few dicopper(II) tetracarboxylate complexes viz. [Cu₂(µ-O₂CC₆H₅)₄(4-Etpy)₂] (1), [Cu₂(µ-O₂CC₆H₅)₄(4-DMAP)₂] (2), [Cu₂(µ-O₂CC₆H₅)₄(4-CNpy)₂] (3) and [Cu₂(µ-O₂CCH₃)₄(4-CNpy)₂] (4) have been utilised as catalysts for oxidation of benzyl alcohols using aqueous tert-butyl hydroperoxide as the oxidant. Complexes 1 and 2 have shown better catalytic activity than the other two. Unlike other catalysts, these dicopper complexes can catalyse oxidation of alcohols at a very low concentration (0.5 mol%).     

Nitroxide polymer brushes as efficient and recoverable catalysts for the selective oxidation of primary alcohols to aldehydes

2,2,6,6‐Tetramethylpiperidinyloxyl (TEMPO)‐containing polymer brushes were grafted onto crosslinked polystyrene microspheres via surface‐initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of 2,2,6,6‐tetramethyl‐4‐piperidyl methacrylate, followed by an oxidation process with 3‐chloroperoxybenzoic acid as oxidant. The synthesized nitroxide polymer brushes included homopolymer brushes, block copolymer brushes, and random copolymer brushes with various TEMPO contents and molecular weights. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. These nitroxide brushes bearing high TEMPO contents were used as recoverable catalysts for the hypochlorite and aerobic oxidation of primary alcohols to aldehydes. The effects of polymer brush structure on the catalytic properties were studied and discussed. The results showed that these nitroxide polymer brushes had excellent catalytic properties and good recycling performances. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44365.     

Novel cobalt-doped ZrSnO4 catalysts for direct nitrous oxide decomposition

Novel ZrSn_1−xCo_xO_4−δ catalysts for the direct decomposition of nitrous oxide (N₂O) were synthesized using a co-precipitation method. Metastable ZrSnO₄ with an α-PbO₂-type structure was used as the mother solid because of its interstitial open spaces derived from its lattice distortion that may be effective for N₂O adsorption. The doping of Co^2+/3+ into the ZrSnO₄ lattice improved the N₂O decomposition activity, likely owing to the enhancement of the redox properties and the increase in the number of oxygen vacancies. Among the prepared catalysts, Zr_1.17Sn_0.73Co_0.10O_4−δ exhibited the highest activity decomposing N₂O completely decomposed at 550°C. In addition, the Zr_1.17Sn_0.73Co_0.10O_4−δ catalyst showed high durability in the presence of CO₂, O₂, and H₂O vapor.     

Cobalt molybdenum oxide catalysts for selective oxidation of cyclohexane

Oxidation of cyclohexane has been carried out using molecular oxygen over cobalt molybdenum oxide (CoMoO₄) catalysts in solvent free conditions. The catalysts were prepared using citrate method with three different molar ratios of Co:Mo, 1:1, 1:2, and 2:1 along with individual oxides for comparative studies. While all the catalysts showed significant activity and selectivity, CoMoO₄ with 1:1 ratio showed the best performance compared to the others with a conversion of 7.38%, with selectivity to cyclohexanol and cyclohexanone (KA oil) of 94.3%, in 1 h. The performance of the catalyst, has been studied as a function of oxygen pressure, reaction temperature, and catalyst loading. It was observed that the catalyst deactivates during the course of the reaction. The reasons for deactivation and methods for restoring the activity have been studied. A kinetic model is presented that captures the complex kinetics and matches well with the experimental data. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4384–4402, 2016     

Electroreduction of nitrous oxide on platinum and palladium: Toward selective catalysts for methanol–nitrous oxide mixed-reactant fuel cells

The kinetics of N₂O electroreduction in the absence and presence of methanol was studied between 295 and 333 K on polycrystalline Pt and Pd electrodes in 0.1 M NaOH. In the absence of methanol the reduction of N₂O on Pd is more facile than on Pt as shown by the approximately four times lower apparent activation energy and lower Tafel slope (Pt: 0.111 ± 0.019 V dec⁻¹, Pd: 0.084 ± 0.007 V dec⁻¹ at 295 K). Two different electroreduction mechanisms are proposed for Pt and Pd with and without participation of underpotential deposited hydrogen, respectively. The selectivity of Pt and Pd electrodes toward both N₂O electroreduction and methanol (0.5 and 1 M) oxidation at 295 K was also investigated. Pt based electrocatalysts are promising candidates for the anode of a mixed reactant CH₃OH–N₂O fuel cell due to inhibition of N₂O reduction by chemisorbed methanol. Pd on the other hand is a selective cathode electrocatalyst since N₂O reduction takes place fairly actively in the presence of 1 M methanol, while methanol oxidation is inhibited.     

Polymer encapsulation of metallophthalocyanines: efficient catalysts for aerobic oxidation of alcohols

Metallophthalocynines (MPcs) of iron, cobalt and copper have been successfully encapsulated for the first time on polystyrene matrix, rendering them highly dispersible in common organic solvents. These catalysts were characterised by diffuse reflectance UV–Vis as well as FT-IR spectroscopy. The encapsulated metallophthalocyanines (MCMPcs) were found to be stable and more active than their unencapsulated counterparts. These encapsulated catalysts showed enhanced activity for aerobic oxidation of alcohols mimicking cytochrome P-450 dependent mono oxygenases. These catalysts not only have high turnover frequencies but could be recovered quantitatively by simple filtration and reused without loss of activity.     

Mesoporous vanadium oxide as catalyst for liquid-phase selective oxidation of diphenylmethane to benzophenone

The mesoporous vanadium oxide (MVO) was prepared from the surfactant cetyltrimethylammonium bromide along with benzyl alcohol as co-surfactant. It was found that the presence of benzyl alcohol in the synthetic mixture was essential to the formation and stability of MVO material. Characteristic mesoporous structure with uniform channel spacing as well as large surface area and pore volume of MVO sample were identified by XRD, SEM, TEM, and N₂ sorption techniques. The structure of vanadium–oxygen framework was explored using FT-IR and ⁵¹V MAS NMR spectroscopy; the MVO sample possessed distorted tetrahedron structure. Results from TPR studies indicated the easier reducibility of MVO as compared to bulk V₂O₅. In the liquid-phase selective oxidation of diphenylmethane to benzophenone in acetic acid as solvent, the MVO catalyst exhibited remarkably better catalytic performance than bulk V₂O₅; at 60 °C, the conversion and benzophenone selectivity reached 39.6 and 96.7% after 1 h reaction time, with a catalyst turnover frequency of 24.2 h⁻¹. These superior results were properly correlated to the physico-chemical properties of MVO catalyst.     

Highly efficient V-Mo-Fe-O catalysts for selective oxidation of toluene to benzaldehyde

The V-Mo-Fe-O catalysts were synthesized by a sol-gel method, characterized and used for the selective oxidation of toluene to benzaldehyde with hydrogen peroxide. The results show that V-Mo-Fe-O catalyst is an effective catalyst, exhibiting a toluene conversion of 40.3%, and a benzaldehyde selectivity of 84.5% at 80 °C. Scanning electron microscopy (SEM) shows that the catalyst has nanorod structure with a thin layer compound, which may be constitutive of iron molybdate while the main compound of catalyst is MoV₂O₈. Furthermore, the catalyst can be easily recycled and reused for four times without significant changes in its activity.     

Mesoporous Co-Al oxide nanosheets as highly efficient catalysts for CO oxidation

We report mesoporous Co-Al oxide nanosheets (Co_xAl-Ns, where x denotes the Co/Al ratio in the samples) prepared by calcination of CoAl-hydrotalcite and subsequent alkaline treatment. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements show that the prepared Co-Al oxide nanosheets (Co_xAl-Ns) are very thin (10–15 nm) and exhibit high mesoporosity (3–5 nm). Catalytic CO oxidation tests reveal that the Co_xAl-Ns exhibit excellent catalytic performances at relatively low temperatures: for example, the Co_2.5Al-Ns catalyst could achieve 99% CO conversion at −98°C. Kinetic studies and experimental investigations indicate that the high activity of the Co_2.5Al-Ns sample is strongly related to the abundance of active sites associated with the large Brunauer–Emmett–Teller surface area. The Co_2.5Al-Ns catalyst also achieves full conversion of CO in tests performed with a gas mixture simulating automobile exhaust gas at 200°C. After loading the Co_2.5Al-Ns on a porous ceramic substrate, the obtained Co_2.5Al-Ns/PC shows high activity and stability in CO oxidation process. These features are potentially important for future industrial applications of these catalysts.     

改性VPO催化剂及其环己烷液相氧化反应性能

采用共沉淀法制备了铋改性钒磷氧催化剂,并用X射线衍射(XRD)、FTIR、SEM等技术对催化剂进行了表征。以环己烷为原料,H2O2为氧化剂,铋改性的钒磷氧化物为催化剂,研究了氧化合成环己醇和环己酮反应,研究了Bi/V比率、P/V比率、溶剂和反应温度等因素对其反应性能的影响。结果表明,Bi/V比率提高时,环己烷转化率,尤其是环己酮的选择性明显提高。P/V比对改性催化剂活性和结构影响较大,P的加入破坏了V2O5的晶型结构,形成大量磷酸盐物种。在Bi/V摩尔比为0.1、P/V摩尔比为0.92、丙酮为溶剂、65℃的反应条件下,反应8h,环己烷转化率为81.4%,环己酮和环己醇的收率分别为58.2%和23.2%。     

Pd/NaY催化苯甲醇无溶剂选择性氧化反应

采用离子交换法将[Pd(NH₃)₄]²⁺交换到NaY分子筛中,经焙烧和氢气还原制备金属钯粒径可调变的Pd/NaY催化剂。在(120~500) ℃改变焙烧温度,可以获得金属钯粒径(1.3~11.9) nm的Pd/NaY催化剂。Pd/NaY催化剂能够催化苯甲醇的无溶剂选择性氧化反应,对含不同钯粒径的Pd/NaY催化剂上醇选择性氧化研究发现,在1.6%Pd/NaY催化剂用量0.1 g、反应温度100 ℃、苯甲醇用量48.5 mmol和O₂流速3 mL·min^-1条件下,苯甲醇转化的真实转化频率随粒径变化在3.2 nm处呈最大值,该反应为结构敏感反应。     

Vanadium oxide catalysts on structured microfiber supports for the selective oxidation of hydrogen sulfide

Vanadium(V) oxide catalysts for the selective oxidation of hydrogen sulfide to sulfur on a nonporous glass-fiber support with a surface layer of a porous secondary support (SiO₂) are studied. The catalysts are obtained by means of pulsed surface thermosynthesis. Such catalysts are shown to have high activity and acceptable selectivity in the industrially important region of temperatures below 200°C. A glass-fiber catalyst containing vanadium oxide (10.3 wt % of vanadium) in particular ensures the complete conversion of H₂S at a temperature of 175°C and a reaction mixture hourly space velocity (RMHSV) of 1 cm³/(g_cat s) with a sulfur yield of 67%; this is at least 1.35 times higher than for the traditional iron oxide catalyst. Using a structured glass-fiber woven support effectively minimizes diffusion resistance and greatly simplifies the scaleup of processes based on such catalysts. Such catalysts can be used for the cleansing of tail gases from Claus units and in other processes based on the selective oxidation of H₂S.     

Advances and perspectives in catalysts for liquid-phase oxidation of cyclohexane

The latest progress and developments in catalysts for the oxidation of cyclohexane are reviewed. Catalytic systems for the oxidation of cyclohexane including metal supported, metal oxides, molecular sieves, metal substituted polyoxometalates, photocatalysts, organocatalysts, Gif systems, metal-organic catalysts and metalloporphyrins are discussed with a particular emphasis on metalloporphyrin catalytic systems. The advantages and disadvantages of these methods are summarized and analyzed. Finally, the development trends in the oxidation technology of cyclohexane are examined.     

室温快速合成HKUST-1应用于醇选择性催化氧化

利用溶剂诱导成核法,将HKUST-1前驱液滴加入甲醇溶液,在室温条件下即可快速合成HKUST-1晶体。X-射线衍射结果表明所合成的HKUST-1具有很高的结晶度;扫描电子显微镜显示该HKUST-1具有规则的八面体形貌,尺寸为2～3μm; N2吸附实验表明HKUST-1的BET比表面积高达1 100 m2/g。利用HKUST-1含有大量的未饱和Cu2+,以HKUST-1和2,2,6,6-四甲基哌啶氧自由基(TEMPO)组成的催化体系,研究了HKUST-1/TEMPO对苯甲醇选择性氧化成苯甲醛的反应。催化结果表明,HKUST-1/TEMPO体系在无外加碱添加剂时,在三氟甲苯溶剂中,可将苯甲醇高效、高选择性氧化成苯甲醛。HKUST-1和TEMPO均是催化苯甲醇转化成苯甲醛的催化剂,两者缺一不可。HKUST-1催化前后结构未发生明显变化,催化剂循环利用4次后,对苯甲醇的转化率仍保持在80%以上,是优异的异相催化剂。     

Characterizations of Ru/ZnO catalysts with different Ru contents for selective hydrogenation of crotonaldehyde

Ru catalysts supported on ZnO with different Ru contents were prepared by an impregnation method and were applied to the vapor-phase selective hydrogenation of crotonaldehyde. The catalysts were characterized by X-ray powder diffraction (XRD), NH₃ temperature-programmed desorption (NH₃-TPD), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). It was found that with increasing Ru contents in the Ru/ZnO catalysts, the activity (TOF), surface acidity amount and deactivation rate increased and the selectivity to crotyl alcohol increased first and then decreased. The 3Ru/ZnO catalyst showed the highest selectivity to crotyl alcohol (up to 88.0%) for the hydrogenation of crotonaldehyde. The initial TOF values of the catalysts depended on the strength of surface acidity and the Ru particle sizes. The more Lewis acid sites made catalysts deactivate more easily. It was assumed that the deactivation was due to the formation of organic compounds deposition and poison effect of CO strongly adsorbed on the Ru atoms.     

室温快速合成HKUST-1应用于醇选择性催化氧化

利用溶剂诱导成核法,将HKUST-1前驱液滴加入甲醇溶液,在室温条件下即可快速合成HKUST-1晶体。X-射线衍射结果表明所合成的HKUST-1具有很高的结晶度;扫描电子显微镜显示该HKUST-1具有规则的八面体形貌,尺寸为2～3μm; N2吸附实验表明HKUST-1的BET比表面积高达1 100 m2/g。利用HKUST-1含有大量的未饱和Cu2+,以HKUST-1和2,2,6,6-四甲基哌啶氧自由基(TEMPO)组成的催化体系,研究了HKUST-1/TEMPO对苯甲醇选择性氧化成苯甲醛的反应。催化结果表明,HKUST-1/TEMPO体系在无外加碱添加剂时,在三氟甲苯溶剂中,可将苯甲醇高效、高选择性氧化成苯甲醛。HKUST-1和TEMPO均是催化苯甲醇转化成苯甲醛的催化剂,两者缺一不可。HKUST-1催化前后结构未发生明显变化,催化剂循环利用4次后,对苯甲醇的转化率仍保持在80%以上,是优异的异相催化剂。     

Selective oxidation of allylic alcohols over highly ordered Pd/meso-Al2O3 catalysts

Highly ordered mesoporous alumina was prepared via evaporation induced self assembly and was impregnated to afford a family of Pd/meso-Al₂O₃ catalysts for the aerobic selective oxidation (selox) of allylic alcohols under mild reaction conditions. CO chemisorption and XPS identify the presence of highly dispersed (0.9–2 nm) nanoparticles comprising heavily oxidised PdO surfaces, evidencing a strong palladium-alumina interaction. Surface PdO is confirmed as the catalytically active phase responsible for allylic alcohol selox, with initial rates for Pd/meso-Al₂O₃ far exceeding those achievable for palladium over either amorphous alumina or mesoporous silica supports. Pd/meso-Al₂O₃ is exceptionally active for the atom efficient selox of diverse allylic alcohols, with activity inversely proportional to alcohol mass.