P对Cu/Al2O3催化剂结构及其催化甘油氢解反应性能的影响

采用分步浸渍法制备了P改性的Cu/Al2O3催化剂,利用N2吸附-脱附、X射线衍射、红外光谱、紫外-可见光谱、H2程序升温还原、NH3程序升温脱附和N2O解离吸附等方法对催化剂进行了表征,考察了P含量及浸渍次序对催化剂结构及其催化甘油氢解反应性能的影响.结果表明,先浸渍P再浸渍Cu时,所制Cu/Al2O3催化剂酸性较高,同时还促进了Cu的分散.随P含量的增加,催化剂的酸量及Cu分散度提高,并且Cu与P物种的相互作用增强;然而,P含量较高时会覆盖Cu,使暴露的Cu表面降低.先浸渍Cu后浸渍P时,尽管也提高了相应催化剂的酸性,但对Cu分散的影响不大,并且还会覆盖Cu使暴露的Cu表面明显降低.先浸渍P明显提高了Cu/Al2O3上甘油氢解反应性能.在220oC,3MPa,质量空速2h?1以及H2/甘油摩尔比20的条件下,当P含量由0增加至6%时,甘油转化率从17.1%升至95.0%,1,2-丙二醇选择性从83.7%升至97.2%.这可归因于催化剂酸性的提高及Cu与P间的相互作用.     

In Situ-Generated,Dispersed Cu Catalysts for the Catalytic Hydrogenolysis of Glycerol

The present study is dedicated to the experimental verification of a concept for the hydrogenolysis of glycerol over in situ-generated Cu dispersed particles (Cu-DP). The Cu-DP were generated by in situ reduction of a precursor salt (Cu(OAc)₂, CuSO₄, CuCl₂) in the presence of KOH and were active in glycerol conversion under hydrogen (T = 200–220 °C, p(H₂) = 1–4 MPa), where 1,2-propylene glycol (PG) and lactic acid (LA) were detected to be the main products. The influence of the reaction conditions (temperature, hydrogen pressure, reaction time, catalyst-to-feed ratio and the KOH/Cu ratio) on the yields of the products is described. It was shown that the selectivity between the PG and LA could be tuned by changing p(H₂) or by the KOH amount, i.e., higher yields of LA corresponded to lower p(H₂) and higher alkalinity of the reaction media. The activity of the in situ-generated Cu-DP was found to be comparable to that of an industrial Cu-Cr₂O₃ catalyst. The Cu-DP catalysts were characterized by XRD, XPS, HRTEM and SEM. During the reaction, the catalyst evolved by the sintering and recrystallization of the separate Cu-DP; the crystallite sizes after 1 and 15 h reaction times amounted to 35 and 49 nm, respectively.     

FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

Catalytic oxidation of unsymmetrical dimethylhydrazine on Pt/SiO<Subscript>2</Subscript>

Specific features of oxidation of unsymmetrical dimethylhydrazine on a Pt-containing catalyst were studied. The temperature dependence of the unsymmetrical dimethylhydrazine conversion was determined, and the main intermediate and final reaction products were identified. Platinum behaves in the process as a multifunctional catalyst participating in dehydrogenation, hydrogenolysis, and oxidation. A new method was suggested for detecting unsymmetrical dimethylhydrazine in air. It consists in catalytic conversion of unsymmetrical dimethylhydrazine and detection of the nitrogen dioxide formed with semiconductor gas sensors. The method was successfully used for detecting unsymmetrical dimethylhydrazine in air at concentrations in the range 0.1–10 mg m^–3.     

Preparation of CuO/SiO<Subscript>2</Subscript> Hollow Spheres for Catalytic Oxidation of Phenol

Porous CuO/SiO₂ hollow microspheres were synthesized via an impregnation method using pure SiO₂ hollow microspheres as the supporter, and Cu species as the functional material. The hollow microspheres were characterized by X-ray diffraction, BET surface area, temperature-programmed reduction, transmission electron microscopy, and scanning electron microscopy. The catalytic activities of the CuO/SiO₂ hollow microspheres were investigated via the removal of the total chemical oxygen demand (COD) in the oxidation of phenol solution with air as an oxidant. The influence of various reaction parameters such as the reaction temperature, the partial pressure of O₂, and the initial pH of the solution were studied in detail. The coordination, dispersion and aggregation degree of copper species on porous materials play an important role for the COD removal of the phenol aqueous solution.     

镧助剂对铜硅催化剂结构及其甘油氢解性能影响研究

在沉淀凝胶法制备的Cu/SiO2催化剂中采用浸渍法添加La助剂,制备了一系列不同La含量的Cu-La2O3/SiO2催化剂,利用BET、XRD、TPR、XPS和TEM对催化剂进行了系统表征,并在高压反应釜中对其进行了甘油氢解制备1,2-丙二醇活性评价,研究了La含量对催化剂高温热稳定性及甘油氢解活性的影响.结果表明:适量La的引入能明显抑制催化剂的高温烧结,维持催化剂的大比表面及活性组分的高分散,提高催化剂的结构稳定性;同时对减少反应过程中活性组分的流失也有很好的效果.铜镧之间存在着协同作用,经高温焙烧后得到加强,对Cu/SiO2催化剂的甘油氢解活性有很好的促进作用.     

Nanosized TiO<Subscript>2</Subscript> particles decorated on SiO<Subscript>2</Subscript> spheres (TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>): synthesis and photocatalytic activities

Nanosized TiO₂ and nano-anatase TiO₂ decorated on SiO₂ spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO₂ nano particle and TiO₂ grafted on SiO₂ sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO₂/SiO₂ particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO₂ particles.     

Structure and Catalytic Properties of Ceria-based Nickel Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina. The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance also depends on the crystal structure of Ni–Ce–ZrO₂. For example, nickel catalysts co-precipitated with Ce_0.8Zr_0.2O₂ having cubic phase gave synthesis gas with CH₄ conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO₂ having tetragonal phase (Ce_0.8Zr_0.2O₂) or mixed oxide phase (Ce_0.5Zr_0.5O₂) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst is attributed to a combination effect of nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂ support and the finely dispersed nano size NiO _x crystallites, resulting in the intimate contact between Ni and Ce_0.8Zr_0.2O₂ particles. The Ni/Ce–ZrO₂/θ–Al₂O₃ also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO₂ resulting in the existence of stable NiO _x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results further confirmed that NiO _x formation was more favorable than NiO or NiAl₂O₄ formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support. Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO₂/CH₄ ratio and H₂O and/or O₂ addition were also examined.     

Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Effect of the preparation conditions on the physicochemical and catalytic properties of Ni<Subscript>2</Subscript>P/SiO<Subscript>2</Subscript> catalysts

The effect of the reduction conditions on the physicochemical and catalytic properties of Ni₂P/SiO₂ catalysts was studied. The catalysts were prepared by impregnating silica with a solution of nickel acetate and diammonium hydrogen phosphate followed by drying, calcination, and temperature-programmed reduction. The Ni₂P/SiO₂ catalysts were reduced prior to hydrodeoxygenation (HDO) of methyl palmitate in the catalytic reactor (in situ) at temperatures of 550, 600, and 650 °С for 3 h and at 600 °С for 1 and 6 h. The reduction temperature and reduction time were shown to affect the conversion of methyl palmitate, and the optimal reduction conditions of the Ni₂P/SiO₂ catalysts were found. The Ni₂P/SiO₂ catalyst synthesized according to a widely used preparation method, including steps of passivation and rereduction at 450 °С in addition to the reduction step, is inferior in activity to the samples prepared in situ.     

Fabrication,characterization, and photocatalytic performance of TiO<Subscript>2</Subscript> hybridized with SiO<Subscript>2</Subscript>

Nanostructures TiO₂–SiO₂ photocatalysts were successfully synthesized using the sol-gel method, hydro-calcination, co-precipitation and room-temperature solid-phase synthesis technology. X-ray powder diffraction pattern (XRD), Fourier transform infrared spectrum (FTIR), photoluminescence (PL) spectra, thermal analyses (TG–DTA), scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) were used to characterize the as-synthesized catalysts. Photocatalytic performances of the catalysts were evaluated by the degradation of methyl orange (MO) under s imulated natural light and the degradation rate of MO is 97.2%. The composites showed a good stability: after five recycling runs there are no significant decreases in the photocatalytic activity. The photodegradation of methylene blue, rhodamine B, methyl violet, naphthol green B, basic fuchsin, malachite green, and methyl red were also tested, and the degradation rate of dyes could reach over 94.2 %. A possible mechanism for the photocatalysis with the TiO₂–SiO₂ was proposed.     

Bimetallic Pt<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>/SiO<Subscript>2</Subscript> Catalyst: Preparation,Structure, and Properties in Preferential Oxidation of Carbon Monoxide

The Pt_0.5Со_0.5/SiO₂ catalyst has been prepared by the decomposition of a [Pt(NH₃)₄][Co(C₂O₄)₂(H₂O)₂]. 2H₂O binary complex salt supported in the pores of SiO₂ pellets. It has been shown by a complex of physical and chemical methods that Pt_0.5Со_0.5/SiO₂ contains alloy nanoparticles with an average composition Pt0.5Co0.5. The catalytic properties of Pt_0.5Со_0.5/SiO₂ are studied in the preferential oxidation of СО in the reaction mixtures with various compositions. It was found that Pt_0.5Со_0.5/SiO₂ has a high selectivity and makes it possible to decrease the outlet concentration of CO to a level of <10 ppm, and the presence of СО₂ and/or Н₂О in the reaction mixture almost does not affect its catalytic properties. The structure of the catalyst is stable under the conditions of preferential CO oxidation.     

TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hybrid nanomaterials: synthesis and variable UV-blocking properties

Silica and core–shell structured titania/silica (TiO₂/SiO₂) nanoparticles with particles size ranging from tens to hundreds of nanometers were prepared and deposited onto cotton fabric substrates by sol–gel process. The morphologies of the nanoparticles were characterized by field-emission scanning electron microscope (FE-SEM). The photocatalytic decomposition properties as well as UV-blocking properties of the fabrics treated with SiO₂ and TiO₂/SiO₂ nanoparticles were investigated.     

Study of the Influence Exerted by Zinc Additive on the Structure and Catalytic Properties of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Liquid-Phase Hydrogenation of Acetylene

Effect of the phase composition of aluminum oxide [γ- and (δ + θ) phase] and introduction of zinc additives on the catalytic properties of 0.5% Pd/Al₂O₃ systems in the reaction of liquid-phase hydrogenation of acetylene into ethylene under an elevated pressure in a flow-through mode was studied. An increase in the activity of the Pd catalyst upon modification with zinc is only observed in the case of a system supported by the mixed phase of (δ + θ) aluminum oxide. XAFS spectroscopy was used to find that the increase in the activity and selectivity with respect to ethylene (in the presence of carbon monoxide) on the (0.5% Pd–0.62% Zn)/(δ + θ)-Al2O3 catalyst is correlated with the formation of the PdZn intermetallic compound.