Effect of water treatment and Ce doping of Pt/Al2O3 catalysts on Pt sintering and propane oxidation

The effect of Ce doping and pretreatment of Pt/Al₂O₃ on its catalysis of propane oxidation was investigated after aging the catalysts. The Ce amount and pretreatment conditions were varied, and the propane oxidation activity was measured. The properties of the catalysts were investigated by means of XRD, STEM-EDX, FT-IR, and H₂-TPR. The size of the Pt nanoparticles (PtNPs) decreased for water-treated catalysts doped with a small amount of Ce, suggesting that water treatment of Ce-doped catalysts inhibits Pt sintering. The minimum PtNP size was obtained with ca. 3.6 wt% of Ce. The Ce species with less than 3.6 wt% existed in a dispersed state, whereas above this value, CeO₂ particulates co-existed. The propane oxidation temperature of the water-treated catalysts was lowered to an extent that depended on the Ce content. This tendency is consistent with the PtNP size in the catalysts. It is considered that highly dispersed Ce species take a primary role in promoting propane oxidation on PtNPs. The reduction temperature of Ce species on water-treated catalysts was lower than that of untreated catalysts, probably owing to a stronger interaction between Pt and Ce, demonstrated by FT-IR measurements. The increased reducibility of Ce species may be the reason for the improved oxidation activity of the catalysts.

Graphic abstract

     

Importance of catalyst–photoabsorber interface design configuration on the performance of Mo-doped BiVO4 water splitting photoanodes

Photoelectrochemical water splitting is mostly impeded by the slow kinetics of the oxygen evolution reaction. The construction of photoanodes that appreciably enhance the efficiency of this process is of vital technological importance towards solar fuel synthesis. In this work, Mo-modified BiVO₄ (Mo:BiVO₄), a promising water splitting photoanode, was modified with various oxygen evolution catalysts in two distinct configurations, with the catalysts either deposited on the surface of Mo:BiVO₄ or embedded inside a Mo:BiVO₄ film. The investigated catalysts included monometallic, bimetallic, and trimetallic oxides with spinel and layered structures, and nickel boride (Ni_xB). In order to follow the influence of the incorporated catalysts and their respective properties, as well as the photoanode architecture on photoelectrochemical water oxidation, the fabricated photoanodes were characterised for their optical, morphological, and structural properties, photoelectrocatalytic activity with respect to evolved oxygen, and recombination rates of the photogenerated charge carriers. The architecture of the catalyst-modified Mo:BiVO₄ photoanode was found to play a more decisive role than the nature of the catalyst on the performance of the photoanode in photoelectrocatalytic water oxidation. Differences in the photoelectrocatalytic activity of the various catalyst-modified Mo:BiVO₄ photoanodes are attributed to the electronic structure of the materials revealed through differences in the Fermi energy levels. This work thus expands on the current knowledge towards the design of future practical photoanodes for photoelectrocatalytic water oxidation.

     

Polymerization of 1-Ethynyl-1-Cyclohexanol by Transition Metal Catalysts

Abstract

The polymerization of 1-ethynyl-l-cyclohexanol (ECHO) was carried out by various transition metal catalysts. The Mo- and W-based catalysts gave a relatively low yield of polymer (≤32%). The catalytic activity of Mo-based catalysts was greater than that of W-based catalysts. PdCl₂ was a very effective catalyst for the present polymerization and gave a high yield of polymer. (Ph₃P)₂PdCl₂ and PtCl₂ were also found to be effective catalysts. The structure of the resulting poly(ECHO) was identified by various instrumental methods as a conjugated polyene structure having an α-hydroxycyclohexyl substituent. The poly(ECHO)s were mostly light-brown powders and completely soluble in various organic solvents such as chloroform, chlorobenzene, benzene, DMSO, and THF. Thermal and morphological properties were also studied.     

Sodium and potassium halides as catalysts for the addition of carbon dioxide to epoxides: the effect of co-solvents

A complex study of sodium and potassium halides as catalysts of the addition of CO₂ to epoxides to yield organic carbonates was carried out. The activity of these metal iodides was investigated. The conditions allowing achievement of a quantitative conversion of epoxides into carbonates were found by varying the temperature, carbon dioxide pressure, and available co-solvents.

     

Effect of promoter on selective hydrogenation of furfural over Cu-Cr/TiO2 catalyst

The selective hydrogenation of furfural has been investigated over the titania-supported monometallic (Cu) and bimetallic (Cu–Cr) catalysts. The catalytic performances were assessed over 4 h of run length under atmospheric pressure at the hydrogen-to-hydrocarbon ratio of 10.6 and 453 K. The results represented that the level of furfural conversion over the non-promoted catalyst was very low (below 10%) while the promoted one showed considerable furfural conversion during this period (higher than 70%). However, both catalysts exhibited high durability and selectivity towards furfuryl alcohol.

     

Novel Preparation of Polyethylene from Nano‐extrusion Polymerization Inside the Nanochannels of MCM‐41/MgCl2/TiCl4 Catalysts

The MCM‐41 and SiO₂ supported TiCl₄ and TiCl₄/MgCl₂ catalysts with different molar ratios of Mg/Ti were synthesized and used for ethylene polymerization under atmospheric pressure. The nanochannels of MCM‐41 serve as nanoscale polymerization reactor and the polyethylene nanofibers were extruded during the reaction. The nanofibers were observed in SEM micrographs of resulting polyethylene. The effect of MgCl₂ on catalytic activity and thermal properties of resulting polyethylene is investigated too. In the presence of MgCl₂, the catalytic activity increased and more crystalline polyethylene with higher melting points were formed. However, no fibers could be observed in the polyethylene prepared by SiO₂ supported catalysts.     

Sulfide Catalysts for Production of Motor Fuels from Fatty Acid Triglycerides

Patents dealing with the production of motor fuel components by hydrodeoxygenation of renewable raw materials based on fatty acid triglycerides are analyzed. Various methods of using sulfide catalysts in hydrodeoxygenation of fatty acid triglycerides and of their mixtures with petroleum fractions are described. The ways to overcome problems that arise in hydrodeoxygenation, based on using sulfide catalysts differing in the active component and support composition, are considered. For example, the use of supported MoS₂ catalysts free of Co and Ni ensures the conversion of fatty acid triglycerides along the “direct hydrodeoxygenation” pathway to avoid the formation of carbon oxides and related process problems. The use of sulfide catalysts on zeolite-containing supports allows synthesis of products with improved low-temperature properties due to isomerization (or mild hydrocracking) of С₁₅–С₁₈ alkanes formed by hydrodeoxygenation of fatty acid triglycerides.

     

Selective hydrogenation of o-chloronitrobenzene (o-CNB) over supported Pt and Pd catalysts obtained by laser vaporization deposition of bulk metals

Carbon nanotubes (CNTs), γ-alumina (γ-Al₂O₃) and silica (SiO₂) supported Pt and Pd catalysts were produced by laser vaporization deposition of respective bulk metals. The catalysts were characterized by inductive coupled plasma emission spectrometer (ICP), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalytic properties of the catalysts were investigated in the liquid phase hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) under 333 K and 1.0 MPa hydrogen pressure. The results show that the catalytic properties are greatly affected by the supports. Pt/CNTs catalyst exhibits the best catalytic performance among the Pt-based catalysts, producing o-CAN with 99.6% selectivity at complete conversion. Pd/CNTs catalyst exhibits the best catalytic performance among the Pd-based catalysts, giving o-CAN with 95.2% selectivity at complete conversion. For Pt-based catalysts, geometric effect and the textures and properties of the supports play important roles on catalytic properties. On the other hand, geometric effect, electronic effect and the textures and properties of the supports simultaneously influence the catalytic properties of the Pd-based catalysts. In addition, hydrogenolysis of the C–Cl bond can be well inhibited over all catalysts prepared by laser vaporization deposition.     

Differential Thermal Analysis as an Acidity Probe in Zeolite Catalysts

Abstract

Differential thermal analysis is used as an acidity strength probe for a series of mordenite (zeolite) catalysts via determining the temperature at which presorbed pyridine completely desorbs from the catalyst. The findings obtained for metal(s) containing mordenite catalysts have been correlated with the Pearson's assumption concerning Lewis acids and bases and the Pauling's electronegativity of the metals contained and found compatible.

The investigated catalysts can be arranged in their observed order of acidity strength as follows: HTI > Th-HM > Re-HM > Pt-HM > Pt-Th-HM > Pt-Re-HM.     

Study of the Acid-Base Properties of sio2-Supported Nimoo4 Catalysts by Temperature-Programmeddesorption. Effect of the Active Phase Content

The acid-base properties of a series of SiO₂-supported NiMoO₄ catalysts were investigated by temperature-programmed desorption of NH₃ and CO₂. Results show that supported catalysts with ca. one monolayer of the active phase are less acidic than the unsupported stoichiometric NiMoO₄.     

Synthesis and Characterization of Poly(2,2-Dipropargyl-1,3-Propylene Benzaldehyde Acetal) Containing a Bulky Acetal Structure

Abstract

Poly(2,2-dipropargyl-1,3-propylene benzaldehyde acetal) (PDPBA), a cyclopolymer containing a bulky acetal functional group, was prepared with transition metal catalysts. MoCl₅ was found to be the most effective catalyst, and any cocatalyst effect was hardly observed. Polymerization was quantitatively carried out under mild conditions (30°C, M₀ = 0.125) with MoCl₅-based catalysts. The structure and physical properties of the resulting polymer were investigated. The spectral data indicated that the polymer contains alternating double and single bonds along the polymer backbone and a cyclic recurring unit with spiro acetal group. The polymer was completely soluble in common organic solvents. The M _n value of the polymer was in the 70,000 to 80,000 range relative to polystyrene standards by GPC. In addition, the polymer possessed good thermal and oxidative stability. The electrical conductivity of the undoped polymer was 10^?12 S/cm.     

Impact of Geometric Changes on the Oxidation of Catechol by Copper(II) Complexes

Abstract

The synthesis of transition metal complexes which can serve as catalysts for the oxidation of organic molecules involves the search for both more efficient and more selective catalysts.¹ The design of complexes in which structural and electronic features are selectively varied allows the analysis of structure/activity relationships in the study of their oxídation chemistry. Successful probing of these features would therefore allow a more fundamental understanding of the catalysts' properties.

We are particularly interested in the air oxidation of catechol to quinone (shown below), since this is one of the reactions catalyzed by the copper-containing enzyme tyrosinase.²     

The Effect of Chemical Reducing Agents in the Synthesis of Sol-Gel Ru-Sn Catalysts: Selective Hydrogenation of Cinnamaldehyde

The influence of chemical reduction on the properties of bimetallic Ru-Sn/SiO₂ catalyst was studied. Prepared sol-gel catalysts were reduced by NaBH₄, KBH₄, H₂, and CH₂O. Physical and catalytic properties of reduced catalysts were compared to non-reduced ones in the liquid-phase hydrogenation of cinnamaldehyde. The influence of boron impregnation was investigated. The observed hydrogenation activity and selectivity towards cinnamylalcohol were effected by reduction pretreatment. The NaBH₄ reduced catalyst exhibited the highest activity and selectivity. Reduction pretreatment influenced the pore sizes, active metal surface as well as content of carbon impurities. Traces of the reduction agents were detected in the catalysts. Boron impregnation presumably improved the catalyst activity, but had a minor effect on the selectivity.     

Bis(imino)pyridine–iron(II) complexes for ethylene polymerization

Ethylene polymerization was carried out using new late transition metal 2,6-bis(imino)pyridine catalysts containing different substituents (H, NO₂, and OCH₃) at the para position of the pyridine ring, activated by methylaluminoxane. Effects of polymerization parameters such as ethylene pressure, reaction temperature, hydrogen concentration and structure variation on the catalysts activities and polymer properties were investigated. Introducing the functionality in the para-position of the pyridine ring of the catalysts had remarkable effect on the polymer properties as well as the catalysts activities.     

氧化铝载体和氧化钡助剂对钌基氨合成催化剂结构和性能的影响

采用不同来源γ-Al2O3(市售Al2O3-1,合成Al2O3-2)作为钌基氨合成催化剂载体,利用浸渍法制备了一系列添加不同BaO助剂含量的Ba-Ru/Al2O3催化剂.通过X射线衍射(XRD)、N2-低温物理吸附、X射线荧光光谱(XRF)、透射电镜(TEM)、H2程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)和X射线光电子能谱(XPS)等方法研究了不同来源的Al2O3以及BaO助剂含量对负载型钌基催化剂的物相结构、织构性质、微观形貌、表面性质和催化剂的氨合成活性等方面的影响.结果表明,载体的物理化学性质对制备的钌基氨合成催化剂的结构以及活性有较大影响.BaO助剂对催化剂的影响主要表现在两个方面:添加量不同导致BaO与γ-Al2O3的作用力不同,从而进一步影响催化体系的比表面积和孔结构性质;BaO助剂会对体系的Ru物种还原性质以及催化剂表面酸碱性质进行调节,适量BaO的加入能够极大提高反应活性,而这种最佳量与载体性质密切相关.     

CYCLIZATION OF ISOMERIC BUTENYL PHENYL SULFIDES ON CHROMIC CATALYSTS

Abstract

It is established that isometric butenyl phenyl sulfides on chromic catalysts yield mainly direct cyclization products unlike their reactions on heterogenous acidic catalysts previously investigated in our laboratory. In the presence of such catalysts the formation of cyclic comcounds proceeds in different ways depending on the position of the side-chain double bond. In case chromic catalysts are used the mentioned factor affects only the easiness of cyclization, but not the nature of the process as such.     

Synthesis and characterisation of mesoporous hybrid silica-polyoxometalate aerogels for photocatalytic degradation of rhodamine B and methylene blue

ABSTRACT

Mesoporous silica aerogel/polyoxometalate hybrids were successfully synthesised under mild conditions, and were investigated towards photocatalytic degradation of Rhodamine B and Methylene Blue dye models in aqueous media under ultraviolet irradiation. The materials were characterised, in the solid state, by various tools such as FTIR, TGA, and powder XRD, in order to gather information about their chemical and structural properties. Moreover, UV-Vis, AAS, BET, SEM, and EDX techniques were used to confirm the polyoxometalates’ loading and their distribution onto the silica aerogels’ surface. The most important analytical technique was the Nitrogen adsorption-desorption, which revealed a significant increase in the specific surface area and pore volume of the hybrid catalysts after immobilisation. The synthesised hybrid catalysts, TEOS/PW₁₂ and TEOS/SiW₁₂, have shown efficient photocatalytic activity towards Methylene Blue and Rhodamine B degradation within 120 min under ultraviolet illumination, thus reaching a degradation percentage of 81–98% and 55–90%, respectively. UV-Vis analysis was employed to scrutinise the formation of intermediate species and revealed that the photocatalytic degradation process proceeded to completion within a surprisingly short time of ~5 min.     

Synthesis of Highly-Dispersed Ni/Mesoporous Silica via an Ammonia Evaporation Method for Dry Reforming of Methane: Effect of the Ni Loadings

Mesoporous silica was used in conjunction with the ammonia evaporation method to prepare highly dispersed Ni catalysts for the dry reforming of methane (DRM). The effect of Ni dispersion on the catalytic performance was investigated by applying different Ni loadings. The pore structure, morphology, Ni dispersion, catalytic activity for DRM as well as the coke resistance were investigated. During the reaction at a relatively low temperature of 600 °C, all the three catalysts exhibited high stability in CH₄ and CO₂ conversion and excellent coke resistance, in comparison to Ni/SiO₂ catalyst prepared by the incipient wetness method. Among them, 10% Ni–SiO₂ exhibited the best catalytic performance with the maximum steady conversions of 62% and 69% for CH₄ and CO₂ at 600 °C, which was beneficial from its optimal Ni content and the presence of highly-dispersed metal nanoparticles confined in the mesopores.

     

Ni/Fe物质的量的比对Ni-Fe催化剂表面性质和二硝基甲苯加氢活性的影响

采用Fe粉置换氯化镍溶液中的Ni²⁺制备了Ni-Fe催化剂, 并应用于催化二硝基甲苯加氢合成甲苯二胺的反应中。运用XRD、低温氮吸附-脱附、H₂-TPD、XPS和TEM等技术手段对不同Ni/Fe物质的量的比(n_Ni/n_Fe)下催化剂进行了表征。结果表明, n_Ni/n_Fe对Ni-Fe催化剂表面性质影响显著。当n_Ni/n_Fe为1:4时, Fe抑制Ni氧化的作用达到最大, Ni-Fe催化剂化学氢吸附量和活性物种Ni的分散度分别达到了0.16 mmol·g^-1和23%, 催化剂性能得到较大的提升。在优化的催化剂制备条件下, DNT(二硝基甲苯)的转化率和TDA(甲苯二胺)的选择性分别达到了~100%和99%。另外, 对Ni-Zn漆原镍(Urushibara Ni)催化剂和Ni-Fe催化剂催化DNT加氢反应进程进行了研究, 发现它们有相同的加氢中间产物, 但反应不同阶段的催化速率存在差异。     

Stereoregular Polymerization of Alkyl Propiolate Catalyzed by Rh Complex

Abstract

The polymerizations of alkyl esters of propiolic acid by Rh complex catalysts were investigated. [Rh(norbornadiene)Cl]₂, which was the most active among the catalysts examined, gave rise to poly(alkyl propiolate) in a fairly high yield (～80%) in the presence of alcohol as the polymerization solvent. The polymers formed were a pale yellow powder soluble in common organic solvents except for poly(methyl propiolate). The structures of the polymers obtained were investigated by IR, ₁₃C-NMR, CP MAS ₁₃C-NMR, and laser Raman spectroscopies, together with the x-ray diffraction method. Based on these spectroscopic data, it was concluded that this Rh complex can be called a stereoregular polymerization catalyst of alkyl propiolate because the poly(alkyl propiolate) obtained has a cis-transoidal structure.