钒掺杂铜基、铁基双金属催化剂的非均相芬顿氧化性能

为了合理设计有效的非均相芬顿催化剂,本研究采用溶剂热法合成了两种钒掺杂双金属催化剂,并比较了它们的非均相芬顿降解亚甲基蓝的性能。还通过扫描电子显微镜（SEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）等技术手段对样品进行了表征。结果显示,两种催化剂对酸性到碱性（pH=3~10）的亚甲基蓝溶液均有较好的降解效果,Cu-V复合材料在pH=10时对亚甲基蓝的去除率最高,达到95.60%;Fe-V复合材料在pH=3时对亚甲基蓝的去除率最高,达到96.60%。Cu-V、Fe-V复合材料均具有良好的重复利用性,在pH=7的条件下连续运行六次后,对亚甲基蓝的去除率仍分别保持在79.16%和68.22%。对催化反应体系的机理进行了初步探讨,羟基自由基是主要的活性物种,两种催化剂的催化机理略有不同。     

Hydrodesulfurization of dibenzothiophenes over molybdenum catalyst supported on TiO2–Al2O3

Composite types of TiO₂–Al₂O₃ supports, which are γ-aluminas coated by titania, have been prepared by chemical vapor deposition (CVD), using TiCl₄ as a precursor. Then supported molybdenum catalysts have been prepared by an impregnation method. As supports, we employed γ-alumina, anatase types of titania, and composite types of TiO₂–Al₂O₃ with different loadings of TiO₂. We studied the conversion of Mo from oxidic to sulfidic state through sulfurization by X-ray photoelectron spectroscopy (XPS). The obtained spectra unambiguously revealed the higher reducibility from oxidic to sulfidic molybdenum species on the TiO₂ and TiO₂–Al₂O₃ supports compared to that on the Al₂O₃ support. Higher TiO₂ loadings of the TiO₂–Al₂O₃ composite support led to higher reducibility for molybdenum species. Furthermore, the catalytic behavior of supported molybdenum catalysts has been investigated for hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the TiO₂–Al₂O₃ supported Mo catalysts, in particular for the 4,6-dimethyl-DBT, is much higher than that obtained over Al₂O₃ supported Mo catalyst. The ratio of the corresponding cyclohexylbenzene (CHB)/biphenyl (BP) derivatives is increased over the Mo/TiO₂–Al₂O₃. This indicates that the prehydrogenation of an aromatic ring plays an important role in the HDS of DBT derivatives over TiO₂–Al₂O₃ supported catalysts.     

Role of steam in partial oxidation of propylene over a Pd/SDB catalyst

Step-response studies of propylene partial oxidation with oxygen over a hydrophobic Pd/SDB catalyst were conducted at 1000 kPa and 185°C in a fixed-bed reactor. CO₂ was found to be the only oxidation product when the feed contained only propylene and oxygen. CO₂ formation was significantly suppressed by addition of steam to the feed, and this addition leads to the formation of partial oxidation products: acrolein and acrylic acid. A competitive reaction mechanism involving water molecules is proposed to explain the significant influence of steam concentration on the rate of propylene oxidation and product selectivity.     

Catalytic oxidation of hydrocarbons over Co3O4 catalyst prepared by CVD

The total oxidation of C₂H₂, C₃H₆, C₃H₈, n-C₄H₈, n-C₄H₁₀ and i-C₄H₁₀ was studied in a monolithic flow reactor under temperature-programmed mode and highly diluted conditions. The non-catalytic combustion of the investigated hydrocarbons leads to a substantial formation of CO and traces of methane at intermediate temperatures. This drawback was suppressed upon the deposition of a thin layer of Co₃O₄ on the monolith and all investigated hydrocarbons tend to light off at 250–290 °C. The apparent activation energy was found to exhibit a linear correlation with the C–H bond dissociation energy, indicating that the C–H activation is still the rate-limiting step.     

A multi-functional Ru Mo bimetallic catalyst for ultra-efficient C3 alcohols production from liquid phase hydrogenolysis of glycerol

Ru and Mo bimetallic catalysts supported on active carbon modified by phosphotungstic acid (PW) were designed and applied in glycerol hydrogenolysis reaction. The physicochemical properties of the catalysts were characterized and the presence of active sites was investigated from the perspective of the glycerol hydrogenolysis performance. The MoO_x is highly selective for the C—O bond cleavage of glycerol molecules, which can reasonably regulate the strong C—C bond cleavage activity of Ru nanoparticles. By using sequential deposition of Ru and Mo supported on mesoporous PW-C, the characterization results show that the combination of isolated low-valence MoO_x with metal Ru particles can form “MoO_x-Ru-PW”, which provides highly catalytic activity toward C—O bond cleavage, selectively producing more C3 alcohols (mainly 1,2(3)-propanediol). The glycerol conversion of 1% Mo/Ru/PW-C catalyst was 59.6%, the selectivity of C3 alcohol was 96.1%, and the selectivity of propanediol (1,2(3)-propanediol) was 94.9%. It is noteworthy that the selectivity of 1,3-propanediol reached 20.7% when the PW was 21.07% (mass). This study provides experimental evidence for the tandem dehydration and hydrogenation mechanism of the multifunctional Mo/Ru/PW-C catalyst.     

Structure and activity of Au-Pd/SiO2 bimetallic catalyst for thiophene hydrodesulfurization

Monometallic Au, Pd and bimetallic Au-Pd catalysts supported on SiO₂ were prepared by an impregnation method. Their activities on thiophene hydrodesulfurization (HDS) at atmospheric pressure are found to be as a function of calcination temperature of these catalysts. The bimetallic catalyst calcined in air at 400 °C gives the highest activity among them. The techniques including nitrogen physical adsorption, X-ray diffraction, transmission electron microscopy, and X-ray absorption near edge structure were employed to characterize the structure of these catalysts. The results indicate that the effect of gold particles in AuPd/SiO₂ catalyst can facilitate the reduction of PdO phase as well as inhibit the formation of less active Pd₄S phase. The promotional effect of partially oxidative gold and a little of Pd⁰ in AuPd/SiO₂ catalyst is suggested to enhance the HDS activity. The formation of Au_xPd_y alloy phase improves the resistance to sulfur-poisoning of the bimetallic catalyst. The presence of partially oxidized gold particles is considered to be due to the inter-atomic charge transfer from the Au 5d to the Pd 5d band.     

Synthesis of multi-walled carbon nanotubes over tungsten-doped cobalt-based catalyst derived from a layered double hydroxide precursor

Multi-walled carbon nanotubes (CNTs) were prepared over a series of W-doped Co-based catalysts derived from layered double hydroxide precursor by catalytic chemical vapor deposition (CCVD) of acetylene. The materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption experiments and Raman spectroscopy. The effect of the proportion of W in the Co-based catalysts on the carbon yield, diameter uniformity and quality of CNTs was investigated. The results demonstrated that with the increasing W/Co molar ratio from 0 to 1.0, both the mean number of walls and the average diameter of CNT produced over catalysts increased from about 8 to 28 nm and from about 12.1 to 23.7 nm, respectively. A small amount of tungsten added to the catalyst with the W/Co molar ratio of 0.3 could facilitate the dispersion of catalytically active Co species on the surface of support, and thus uniform and high-quality CNTs with a remarkably high yield of ca. 1600% were obtained.     

Gas analysis of the CVD process for high yield growth of carbon nanotubes over metal-supported catalysts

Changes in the gas composition during the methane chemical vapor deposition growth of single- and double-walled carbon nanotubes over metal-supported MgO catalysts were investigated in an attempt to increase the nanotube yield. Monitoring the gas composition by gas chromatography as a function of the reaction time provides information on the activity and lifetime of the catalyst. The degree of methane decomposition, i.e., the C-H bond dissociation, was closely related to the nanotube yield, and the Fe-Mo binary catalyst exhibited a high activity. The effects of water vapor on the catalytic nanotube growth were also studied by introducing water vapor in the inlet gas. An appropriate amount of water prolonged the lifetime of the catalyst and increased the nanotube yield by 35%.     

Design of a C/SiC functionally graded coating for the oxidation protection of C/C composites

To reduce the residual thermal stress between the carbon fiber-reinforced carbon (C/C) composites and the SiC coating layer, functionally graded materials (FGM) consisting of a C/SiC compositionally graded layer (C/SiC interlayer) were adopted. After designing the compositional distribution of the C/SiC interlayer which can relieve the thermal stress effectively, the deposition conditions of the entire compositional range of the C/SiC composites were determined using a thermodynamic calculation. According to the design and calculation the C/SiC interlayer and the SiC outer layer were deposited on the C/C composites by a low pressure chemical vapor deposition (LPCVD) method at deposition temperatures of 1100 and 1300 °C. The stress calculation and the experimental results suggested that the SiC-rich compositional profile in the FGM layer is the most effective for relieving the thermal stress and increasing the oxidation resistance.     

Preferential oxidation of carbon monoxide over Pt, Au monometallic catalyst, and Pt–Au bimetallic catalyst supported on ceria in hydrogen-rich reformate

The objective of this paper was to study a preferential oxidation (PROX) of carbon monoxide over monometallic catalysts including Pt, Au and Pt–Au bimetallic catalyst supported on ceria in hydrogen-rich reformate. Single step sol–gel method (SSG) and impregnation on sol–gel method (ISG) were chosen for the preparation of the catalysts. The characteristics of these catalysts were investigated by X-ray diffractometer (XRD), Brunauer–Emmet–Teller (BET) method, transmission electron microscope (TEM), scanning electron microscope (SEM) and temperature-programmed reduction (TPR). The XRD patterns of the catalysts showed only the peaks of ceria crystallite and no metal peak appeared. From TEM images, the active components were seen to be dispersed throughout the ceria support. The TPR patterns of PtAu/CeO₂ catalyst prepared by SSG showed the reduction peaks were within a low temperature range and therefore, the catalysts prepared by SSG exhibited excellent catalytic activity for preferential oxidation of CO. Bimetallic Pt–Au catalyst improved the activity (90% conversion and 50% selectivity at 90 °C) because of the formation of a new phase. When the metal content of (1:1) PtAu/CeO₂ catalyst prepared by SSG was increased, the CO conversion did not change much while the selectivity decreased in the low temperature range (50–90 °C). The CO conversion increased with increasing W/F ratio. The presence of CO₂ and H₂O had a negative effect on CO conversion and selectivity due to blocking of carbonate and water on active sites.     

Preparation of nickel-on-active carbon catalyst by CVD method for methanol carbonylation

The nickel on active carbon (Ni/A.C.) catalysts prepared by a simple chemical vapor deposition (CVD) method showed comparable catalytic activities for the vapor phase carbonylation of methanol to those of the catalysts prepared by impregnating A.C. with nickel nitrate and activating by hydrogen treatment. The CVD method was successfully applied to the in situ catalyst preparation.     

Multiplicity in the partial oxidation of propylene over a copper-molybdena catalyst

Measurement of rates of formation of acrolein and acetaldehyde in the partial oxidation of propylene over a copper molybdate catalyst were made under steady-state and transient modes. These measurements disclosed a rate of product formation multiplicity apparently attributable to the oxidation state of the catalyst and not to surface phenomena usually thought to be the source of hysteresis in catalytic systems.     

Catalytic performance of Ti-SBA-15 prepared by chemical vapor deposition for propylene epoxidation

Ti-SBA-15C catalysts were prepared by supporting Ti on SBA-15 with chemical vapor deposition (CVD) using TiCl₄ as titanium source, and were characterized by XRD, N₂ adsorption, FT-IR and ICP. The results show that SBA-15E prepared by ethanol solution extracting template has higher concentration of surface Si-OH groups than SBA-15 calcined at 550 °C, resulting in high Ti content on Ti-SBA-15EC prepared by CVD. The temperature and time of TiCl₄ deposition affect the Ti content and catalytic activity of Ti-SBA-15EC for the epoxidation of propylene with cumene hydroperoxide (CHP). Ti-SBA-15EC prepared by CVD at 700 °C for 1.5 h exhibits more excellent performance than Ti-SBA-15C, Ti-SBA-15 prepared hydrothermally and Ti/SBA-15 (impregnation method), and the 87.3% conversion of CHP and 96.4% selectivity to propylene oxide can be obtained at 80 °C for 4 h. The performance of Ti-SBA-15EC is decreased hardly for the epoxidation of propylene after used repeatedly 6 times.     

氧化铒弥散强化氨氧化铂催化剂的制备及性能

通过添加微量金属饵材料到铂网催化剂铂合金中,制成氧化饵弥散强化铂催化剂,与普通二元、三元铂合金丝材相比,常温抗拉强度和延伸率大大提高,抗蠕变性能优异。     

Mass production of high-quality multi-walled carbon nanotube bundles on a Ni/Mo/MgO catalyst

A new catalyst (Ni/Mo/MgO) is reported, with which one can synthesize multi-walled carbon nanotube (MWNT) bundles with a yield of more than 45 times the amount of the pristine catalyst, using a methane-hydrogen mixture as precursor. Powder X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis show that the purity of the as-prepared MWNTs is over 97%. The diameter of the carbon nanotubes is 9-20 nm, measured by high-resolution electron microscopy on 421 individual MWNTs. The high purity of the as-prepared MWNTs allows us to omit the usual complex purification process required for carbon nanotubes synthesized by chemical vapor deposition. Because of its durable high activity, the Ni/Mo/MgO catalyst in its pristine state is ideal for mass production of high-quality MWNTs. The synergism of nickel and molybdenum is considered the main reason for the high yield of carbon nanotubes.     

EQ-101型甲醇氧化制甲醛催化剂的性能评价

EQ-101型甲醛催化剂是一种铁钼系甲醇氧化制甲醛催化剂。考察反应温度、空速和进口甲醇含量等对EQ-101型甲醛催化剂性能的影响;通过500 h稳定性实验,考察EQ-101型甲醛催化剂的活性和稳定性。结果表明,在常压、反应温度300℃、空速12 000 h~(-1)和进口甲醇体积分数6.5%条件下,甲醇转化率99.5%,甲醛收率93.8%;500 h稳定性实验过程中,甲醛收率约稳定在93%,无破碎或粉化现象,催化剂活性和稳定性良好。     

Synthesis of high crystalline beta SiC nanowires on a large scale without catalyst

A simple method was developed for the synthesis of SiC nanowires on a large scale, where the graphite plate and Si–SiO₂ powder mixture were used as the substrate and raw materials, respectively. By this method, pure and high crystalline beta SiC nanowires can be synthesized on the graphite substrate without catalyst. According to the characterization results of XRD, FE-SEM and TEM, it was found that the synthesized nanowires are grown along the [111] orientation and have high crystallinity, clean surface and uniform diameter. And also, it was demonstrated that this method possesses some advantages, such as, low cost and high yield.     

Kinetic studies of the partial oxidation of isooctane for hydrogen production over a nickel-alumina catalyst

The kinetics of the catalytic partial oxidation of isooctane for hydrogen (H₂) production over a stable Ni/γ-Al₂O₃ catalyst was investigated at atmospheric pressure in the temperature range of 863-913 K, ratio of weight of catalyst to the molar feed rate of isooctane in the range of , and molar feed ratio O₂/i-C₈H₁₈ of 4.0 in a 12.7 mm diameter Inconel micro-reactor housed in an electrically controlled furnace. The developed rate models were based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER) formulations. Out of the 18 models developed, 10 were eliminated due to poor predictive efficiency. A LHHW mechanism requiring the dissociative adsorption of isooctane and molecular adsorption of oxygen on a single site was the most likely pathway for the partial oxidation of isooctane. The reaction order of 1.5 indicates a strong coverage of nickel by isooctane.