碳化钨载铂的制备及其对硝基苯的电催化还原

以偏钨酸铵（AMT）为钨源前驱体,气流式喷雾干燥仪造粒,得到空心球状结构偏钨酸铵,固定床气固反应,以CO/CO₂为还原碳化气氛在800℃下制备了介孔空心球状碳化钨。采用氯铂酸作为铂源,用浸渍、气相还原法制备了Pt/WC粉末催化剂。通过XRD和SEM测试手段对Pt/WC粉末样品进行了表征,表明Pt成功负载在介孔WC材料上。采用循环伏安法、以Pt/WC粉末微电极为工作电极,研究了Pt/WC对在质子惰性介质中硝基苯的硝基还原的催化作用。结果表明,Pt/WC催化剂对硝基还原有着良好的电催化活性和化学稳定性。     

新型包覆碳化钨载体负载Pd催化剂的性能

以Vulcan XC-72R活性碳作为碳源,采用高温热处理还原法,在活性碳表面原位还原钨酸铵,形成表面包覆钨的碳化物结构的载体。通过BET等当钨酸铵用量适宜时,形成的钨的碳化物的平均孔径较大,较大介孔所占比例较大,以其为载体制备的Pd催化剂Pd/WC-2其电荷传递阻抗和扩散阻抗都较小。催化剂Pd/WC-2对甲酸的氧化不但具有较高的活性,同时也具有很好的稳定性。     

碳化钨催化剂上烷烃异构化研究进展

综述了用于长链烷烃异构化的碳化钨催化剂的研究进展。介绍了催化剂的制备方法和异构化反应机理。分析了此类催化剂今后的发展趋向和应用前景。     

Preparation of nano-sized tungsten carbide via fluidized bed

Ultrafine or nano-sized of tungsten carbide(WC) is the key material to prepare ultrafine grained cemented carbides. In this paper, nano-sized WC powders were directly prepared by using industrial nano-needle violet tungsten oxide(WO_(2.72)) as the raw material, a fluidized bed as the reactor, and CO as the carbonization gas. The relationship between particle sizes and reaction temperatures, residence times, atmospheres has been investigated systematically. In addition, the physical–chemical indexes(such as residual oxygen, total carbon and free carbon) of the products were measured. The results indicated that the particle size of WC increased with the increase of temperature from 800 to 950 °C. As the residence time increased, the particle size decreased gradually,and then increased due to slight sintering. The introduction of hydrogen reduced the carbonization rate, and is not beneficial to obtaining nano-sized WC. Products that satisfy the standard were obtained when WO_(2.72) reacted with CO at 850 °C, 900 °C and 950 °C for 3.0 h, 2.5 h and 2.0 h, respectively. The particle sizes of the three samples calculated from the specific surface area were 46.4 nm, 53.2 nm and 52.1 nm, respectively.     

碳化钨纳米晶薄膜电极的制备及其对甲醇电氧化性能

引　言碳化钨具有与金属铂相类似的表面电子结构[1], 因此, 人们一直在探索碳化钨在化学领域中的催化性能, 期望利用矿藏丰富、价格低廉的钨矿优势, 用碳化钨来替代资源稀缺、价格昂贵的铂及铂基合金催化剂. 研究表明, 碳化钨在烷烃重整、异构化反应以及在氢析出反应等方面具有     

The multi-structure of oxidized-reduced tungsten carbide surface(s)

The XPS of bulk tungsten carbide, partially oxidized WC surfaces at 373 and 573 K as well as tungsten trioxide have been reported. Bulk WC has been prepared from WO₃ as a starting material in a mixture of CH₄ (20%) and H₂ (80%) at 1150 K for 4 h, while partially oxidized WC surfaces were prepared by oxygen chemisorption on a clean WC surface at 200 K, then the temperatures were raised to 373 and 573 K respectively. The XPS of a freshly prepared WC reveals the presence of a small amount of WO₃ on the surface and a slightly higher concentration in the bulk. The oxygen-exposed fresh WC surfaces and surfaces treated at temperatures higher than 373 K show the presence of WO₃ in a considerable quantity depending on the length and the treatment temperature. Ar⁺ bombardment of this partially oxidized surface reduces WO₃ to WO₂ and W(0), while WC is partially reduced to W(0). Isomerization reactions of alkanes on oxygen-exposed WC surface occurs in reality on a composite surface structure containing WC, WO₃, WO₂ and elemental W(0).     

Nanosecond UV laser induced subsurface damage mechanics of cemented tungsten carbide

The subsurface damage in the laser machining process dramatically affects the mechanical properties and the service life of the cemented tungsten carbide. To further reveal the interaction mechanics, the subsurface damage characteristics of WC/8Co cemented carbide ablated by a nanosecond UV laser is explored through the angle polishing method, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) combined with focused ion beam (FIB) milling. The results show that severe cracking and crushing behaviors appear in the re-solidified areas and the heat-affected zone (HAZ). Based on the temperature field and stress field simulation results, the high temperature gradient induced thermal stress is responsible for the subsurface damage behavior. The blocking of the ablated groove caused by the solidification of the melted material is identified. The XPS spectrums indicate that the machined cemented tungsten carbide is seriously oxidized in the surface and to some extent in the subsurface layer, with the main oxidization products to be WO₃, CoWO₄, WO₂, CoO and Co₃O₄. In addition, the deformation behavior of WC grain and the disordered alignment of Co atoms are identified in the re-solidified area and HAZ.     

Effect of pressure on the electrical resistance flash sintering of tungsten carbide

The application of external pressure during the Electrical Resistance Flash Sintering of tungsten carbide (WC), a “metallic ceramic” with positive temperature coefficient (PTC) for resistivity, results in a limited densification of the powder. In the present work, the effect of pressure on the ultrafast sintering of WC is analysed in detail. In particular, the application of pressure at different stages of flash sintering is studied by varying independently the processing parameters i.e., voltage, time and pressure. Microstructural characterization performed by FE-SEM and XRD identifies biphasic structures of WC and W₂C, which compositions result almost unchanged for different sintering parameters. Increasing the external load from 4 up to 100 MPa leads to microporous materials, limiting the attainable final density. Pressure is demonstrated to control the flash phenomenon directly by affecting the flash duration and intensity, thus controlling the electrical energy dissipated during the power surge with respect to the overall process.     

Catalytic activity and XPS surface determination of tungsten carbide for hydrocarbon reforming. Influence of the oxygen

The influence of oxygen on the catalytic properties of tungsten carbide has been studied for the reforming reaction of 2-methylpentane in a great excess of hydrogen . The oxygen surface concentration has been measured by the ratio of the signal area of the O_1s and the W_4f levels as determined by X-ray photoelectron spectroscopy. Two kinds of processes are observed: cracking and isomerization reactions. The introduction of oxygen at T=350°C leads to a deep decrease of the cracking reaction kinetics; about two orders of magnitude. The tungsten carbide, strongly selective for cracking reactions in absence of oxygen, becomes very selective for isomer production in the presence of oxygen.     

碳纳米管、碳化钨在直接法合成过氧化氢中的应用

选用新型纳米材料——碳纳米管（CNTs）作为催化剂载体,用沉积沉淀法制备负载型钯-铂合金催化剂。同时选用过渡金属碳化物材料（碳化钨）为催化剂,其具有类似于Pt的表面电子结构,有望替代贵金属催化剂。探讨了Pd-Pt/CNTs及碳化钨在氢氧直接合成过氧化氢反应中的催化性能。     

纳米碳化钨的合成及其电催化活性研究

以钨酸和丙烯腈为原料,采用共沉淀法合成碳化钨（WC）前驱体,于H₂和Ar混合气氛中高温还原碳化制备纳米WC。采用傅立叶红外光谱、X射线衍射及扫描电镜等对试样进行表征,在酸性介质中采用循环伏安法测试Pt/WC电化学催化活性。结果表明,实验合成了较纯的纳米碳化钨,其颗粒形貌近似球形,粒径80 nm左右。Pt/WC的电化学表面积（ESA）较传统的Pt/C有较大提高,10%Pt/WC电流密度为51.2 mA·cm^-2。     

Initial stage sintering of binderless tungsten carbide powder under microwave radiation

This work represents an investigation concerning neck growth kinetics during microwave sintering of free-packed spherical shaped binderless tungsten carbide particles. Application of classical sphere-to-sphere approach showed possibility to identify main diffusion mechanisms operating during initial stage of microwave sintering of tungsten carbide powder. An anomalous neck growth in the initial period during microwave sintering was also revealed, which was then followed by neck growth obeying mechanisms of volume and surface diffusion. Numerical simulation of neck growth process revealed anomalous values for diffusion coefficients - 7.16 × 10⁻¹³ and 3.41 × 10⁻⁸ m² s⁻¹ for 950 and 1200 °C respectively. The value of activation energy of neck growth process has been calculated as 69.18 kJ mol⁻¹. That value is significantly lower then any data on activation energy of diffusion processes in W-C system, and may be explained by overheating in the neck zone, or even formation of liquid phase in the neck area.     

超细碳化钨制备过程及机理研究进展

超细碳化钨（WC）具有硬度高、耐磨性好、强度高和韧性较高的特点,是制备硬质合金最基础的原料。因此,超细碳化钨的制备成为学术界和工业界关注的焦点,也是硬质合金制备领域研究的重点。从反应体系的角度综述了超细碳化钨粉体制备技术,对相关反应路径机理进行了分析,并展望了超细碳化钨制备技术的发展趋势。     

Comparison of molybdenum carbide and tungsten carbide for the hydrodesulfurization of dibenzothiophene

The molybdenum and tungsten carbides (Mo₂C and W₂C) were synthesized, characterized and tested in hydrodesulfurization (HDS) of dibenzothiophene (DBT). The phase purity of these catalysts was established by X-ray diffraction (XRD), and the surface properties were determined by N₂ BET specific surface area (Sg) measurements, CO chemisorption and high-resolution transmission electron microscopy (HRTEM). The activities of catalysts were determined during the HDS of DBT at a temperature of 613 K and under a 6 MPa total pressure. Both molybdenum and tungsten carbides were active in HDS of DBT. The reactivity studies showed that molybdenum carbide was more active than tungsten carbide related to weight. However, W₂C was shown to possess stronger hydrogenating properties.     

Comparison between tungsten carbide and molybdenum carbide for the hydrodenitrogenation of carbazole

The activity of molybdenum and tungsten carbides in hydrodenitrogenation (HDN) of carbazole was studied. Transition metal carbides (Mo₂C and W₂C) were synthesized using the temperature-programmed reaction of the appropriate oxide precursor (MoO₃ and WO₃) with the following gas mixture: 10 vol.% CH₄/H₂. The structure of the catalysts was characterized using X-ray diffraction, CO chemisorption, high resolution transmission electron microscopy (HRTEM) and BET surface area measurements. From the HRTEM analysis, it could be concluded that the tungsten carbide was thioresistant in our operating conditions (50 ppm of S, pressure = 6 MPa, 553 < T < 653 K, H₂/feed volumic ratio = 600). In the case of Mo₂C, molybdenum sulphide was observed as single slabs. The activity of catalysts was determined during the hydrodenitrogenation of carbazole at the wide range of temperature (553–653 K) and under a 6 MPa total pressure of H₂. The comparison of tungsten carbide and molybdenum carbide has shown higher activity of Mo₂C than W₂C at the same condition. However, W₂C leads to higher amount of isomers of main products, and have higher hydrogenation activity.     

Tribological performance of binderless tungsten carbide reinforced by multilayer graphene and SiC whisker

Binderless tungsten carbides (BTC) have attracted the attention of both academia and industry due to their excellent hardness, high-temperature strength as well as corrosion resistance. Herein, a set of binderless WC-based composites were developed employing two-step spark plasma sintering. The mechanical response together with tribological performance was investigated as a function of various reinforcements including SiC whisker (SiC_w) and multilayer graphene (MLG). The results suggested that the coupling and synergy of MLG and SiC_w played a critical role in microstructure refinement and homogenization, consequently advancing the mechanical and tribological properties of BTC. The MLG-SiC_w/BTC displayed the optimal comprehensive performances, and the associated toughening and anti-friction mechanisms were determined and analyzed. Such material design offers an effective approach to enhance the mechanical and tribological responses of ceramic materials.     

The electronic structure of oxide-supported tungsten oxide catalysts as studied by UV spectroscopy

The UV spectra of tungsten oxide catalysts supported on alumina, titania and zirconia, and on titania–alumina and titania–zirconia mixed oxides are reported and discussed. Evidence is provided for the different electronic structure of supports and catalysts, which could affect the behavior of the tungsten oxide centres in the different cases. On alumina, tungsten oxide centres are “isolated” by the insulating support, while on titania-based materials they are likely in electronic contact with each other and with Ti centres through the support conduction band. In the case of WOx2013;ZrO₂, the 5d levels of tungsten ions fall just below of the lower energy limit of the support conduction band. This revised version was published online in July 2006 with corrections to the Cover Date.     

工业钛钨粉制备选择性催化还原催化剂的对比研究

以国产和进口专用于制备脱硝选择性催化还原（selective catalytic reduction,SCR）催化剂的工业钛钨粉为原料,采用浸渍法在不同条件下制备了V2O5-WO3/TiO2催化剂,测试了催化剂的脱硝性能,并且采用低温N2吸附法、X射线衍射（XRD）和扫描电子显微镜/X-射线能谱（SEM/EDX）对其结构和组成进行了表征,为提高国产钛钨粉的质量提供依据。实验结果表明,相同条件下国产钛钨粉制备的催化剂脱硝性能稍差于进口,其原因除了原料组成之外,还在于国产钛钨粉制备的催化剂孔容低于进口,活性组分的负载量较低;国产的钛钨粉中有少量的金红石,而且晶粒度较小,烧结程度较进口的大。提高国产钛钨粉的质量,除其组成适当外,还应考虑增大孔容,避免金红石的形成。     

Methane partial oxidation to synthesis gas over bimetallic cobalt/tungsten carbide catalysts and integration with a Mn substituted hexaaluminate combustion catalyst

Co_0.2W_0.8C_x and supported Co_0.2W_0.8C_x catalysts are shown to be active for the partial oxidation of methane to synthesis gas. The catalyst stability is improved by operating at elevated pressure, or in the presence of excess methane. At atmospheric pressure the Co_0.2W_0.8C_x catalysts deactivate by oxidation, as seen by X-ray diffraction. Manganese substituted hexaaluminate catalysts with different Mn contents have been tested as catalysts for the total combustion of methane. In particular BaMn₂Al₁₀O₁₉ is active and stable for the combustion reaction. The temperature rise observed in the reactor was up to 300 K, depending on the reaction conditions, and complete conversion of oxygen in the feed was achieved. A process for stabilising the carbide catalysts is demonstrated, combining the manganese substituted hexaaluminate total oxidation catalyst, in series before the carbide reforming catalyst: this process leads to stable operation, with no carbon formation in the reactor and no carbide catalyst oxidation observed.     

Platinum on nitrogen doped graphene and tungsten carbide supports for ammonia electro-oxidation reaction

Ammonia electrooxidation reaction involving multistep electron-proton transfer is a significant reaction for fuel cells, hydrogen production and understanding nitrogen cycle. Platinum has been established as the best electrocatalyst for ammonia oxidation in aqueous alkaline media. In this study, Pt/nitrogen-doped graphene (NDG) and Pt/tungsten monocarbide (WC)/NDG are synthesized by a wet chemistry method and their ammonia oxidation activities are compared to commercial Pt/C. Pt/NDG exhibits a specific activity of 0.472 mA∙cm^–2, which is 44% higher than commercial Pt/C, thus establishing NDG as a more effective support than carbon black. Moreover, it is demonstrated that WC as a support also impacts the activity with further 30% increase in comparison to NDG. Surface modification with Ir resulted in the best electrocatalytic activity with Pt-Ir/WC/NDG having almost thrice the current density of commercial Pt/C. This work adds insights regarding the role of NDG and WC as efficient supports along with significant impact of Ir surface modification.