氧化钨还原过程及机理研究

利用X射线衍射仪、扫描电镜和比表面仪研究了WO3还原成W粉过程中的相结构、粉末形貌和粒度的演变过程及机理。结果表明WO3在还原过程中依次转变为WO2.90、WO2.72、WO2,最终被还原成W。在WO3氢还原成W粉的过程中,WO3具有的平滑规则六面体形貌会转变为粗糙六面体,并随着还原过程进行,较大的二次颗粒分解成小颗粒。在WO3氢还原成WO2.90和WO2.72的过程中,粉末的比表面积不断增大,粉末粒度不断减小,但在WO2.72还原为WO2和WO2还原为W的过程中,粉末比表面减小,粉末的粒度不断增大。

流态化技术与超细钨粉

本文简要介绍了流态化技术的特点及其在超细钨粉制备中的试验结果,其中包括喷雾干燥所得偏钨酸铵粉(简称 AMT)在流化床炉中的焙烧以及氧化钨在流化床炉中的氢还原的结果.结果表明:流化床炉便于控制钨粉的粒度,尤其适用于制造超细钨粉,其优点是还原速度快,能节省氢气,且利于连续和自动化生产作业.

传统方法制备超细WC粉末的质量控制研究进展

对高品质超细WC粉末制备过程APT煅烧、氧化钨还原、W粉碳化工序的质量控制研究进展进行综述。APT原料的质量与生产过程中工艺参数的控制是超细WC粉末制备的关键。单一性质的APT有利于控制煅烧产物的质量,优化煅烧工艺参数可避免"夹生"硬颗粒;氧化钨还原过程难以控制反应条件一致,多相反应同时发生时控制WO2的生成和还原及W粉的长大是关键;碳化过程既要考虑WC颗粒成分的均匀性,也要考虑晶粒度的均匀性。

Promotional roles of ZrO_2 and WO_3 in V_2O_5-WO_3/TiO_2-ZrO_2 catalysts for NO_x reduction by NH_3:Catalytic performance,morphology,and reaction mechanism

V2O5/TiO2-ZrO2 catalysts containing various amounts of WO3 were synthesized.The catalyst morphologies,catalytic performances,and reaction mechanisms in the selective catalytic reduction of NOx by NH3 were investigated using in situ diffuse-reflectance infrared Fourier-transform spectroscopy,temperature-programmed reduction（TPR）,X-ray diffraction,and the Brunauer-Emmett-Teller（BET） method.The BET surface area of the triple oxides increased with increasing ZrO2 doping but gradually decreased with increasing WO3 loading.Addition of sufficient WO3 helped to stabilize the pore structure and the combination of WO3 and ZrO2 improved dispersion of all the metal oxides.The mechanisms of reactions using V2O5-9%WO3/TiO2-ZrO2 and V2O5-9%WO3/TiO2were compared by using either a single or mixed gas feed and various pretreatments.The results suggest that both reactions followed the Eley-Ridel mechanism;however,the dominant acid sites,which depended on the addition of WO3 or ZrO2,determined the pathways for NOx reduction,and involved[NH4^＋-NO-Bronsted acid site]^＊ and[NH2-NO-Lewis acid site]^＊ intermediates,respectively.NH3-TPR and H2-TPR showed that the metal oxides in the catalysts were not reduced by NH3 and O2did not reoxidize the catalyst surfaces but participated in the formation of H2O and NO2.

WO_x催化剂上正庚烷的临氢异构化反应

采用连续流动固定床反应器考察了WOx催化剂上正庚烷加氢异构化反应性能。详细讨论了还原条件和反应条件对催化性能的影响。采用XRD和BET方法表征了催化剂的物化性质。结果表明,在WOx催化剂上,正庚烷转化率达到20.8%时,其异构化选择性仍然达到86.4%。推测催化剂的活性相为WO2和W3O,催化剂具有中孔结构。

超细和纳米钨粉制备技术进展

超细及纳米钨粉因优越的性能而具有广泛的应用前景,因此其制备技术一直是国内外研究热点。综述了超细和纳米钨粉的制备技术,着重介绍了氧化钨氢还原法、高能球磨法、溶胶凝胶法、冷冻干燥法制备超细及纳米钨粉原理和工艺的应用,并展望了超细和纳米钨粉制备技术的发展趋势。

Solar‐energy‐driven photothermal catalytic C–C coupling from CO_(2) reduction over WO_(3–x)

Solar‐energy‐driven catalytic CO_(2) reduction for the production of value‐added carbon‐based materials and chemical raw materials has attracted great interest to alleviate the global climate change and energy crisis.The production of multicarbon(C2)products through CO_(2) reduction is extremely attractive,however,the yield and selectivity of C2 products remain low because of the low reaction temperature required and the low photoelectron density of the substrate.Here,we introduce WO3–x,which contains oxygen vacancies and exhibits an excellent photothermal conversion efficiency,to improve the generation of C2 products(C2H4 and C2H6)under simulated sunlight(UV‐Vis‐IR)irradiation.WO3–x produced 5.30 and 0.93μmol·g^(–1)C2H4 and C2H6,respectively,after 4 h,with a selectivity exceeding 34%.In situ Fourier transform infrared spectra and theoretical calculations showed that the oxygen vacancies enhanced the water activation and hydrogenation of adsorbed CO for the formation of C2 products via C–C coupling from CH2/CH3 intermediates.The findings of this study could assist in the design of highly active solar‐energy‐driven catalysts to produce C–C coupling products through CO2 reduction.

Photo-thermal CO_(2) reduction with methane on group Ⅷ metals:In situ reduced WO_(3) support for enhanced catalytic activity

Photo-thermal CO_(2) reduction with methane(CRM)is beneficial for solar energy harvesting and energy storage.The search for efficient photo-thermal catalysts is of great significance.Here,we reveal that group Ⅷ metal catalysts supported by optical material WO_(3) are more effective for photo-thermal CRM,giving catalytic activities with visible light assistance that are 1.4-2.4 times higher than that achieved under thermal conditions.The activity enhancement(1.4-2.4 times)was comparable to that achieved with plasmonic-Au-promoted catalysts(1.7 times).Characterization results indicated that WO_(3) was partially reduced to WO_(3-x) in situ under the reductive CRM reaction atmosphere,and that WO_(3-x) rather than WO_(3) enhanced the activities with visible light assistance.Our method provides a promising approach for improving the activity of catalysts under light irradiation.

Controllable synthesis of two-dimensional tungsten nitride nanosheets as electrocatalysts for oxygen reduction reaction

A facile synthetic strategy was developed for insitu preparation of two-dimensional (2D)highly crystalline tungsten nitride (WN)nanosheets with controllable morphology as oxygen reduction reaction (ORR)catalysts.The dependence of the crystal structure and morphology of WN on K2SO4content,pH,and pyrolysis temperature was thoroughly examined.The electrocatalytic performance of WN toward ORR in an alkaline electrolyte indicated that K+plays an important role in the control of size and shape in the hydrothermal and nitridation process,thereby promoting the formation of plate-like WO3and 2D WN nanosheets.The WN nanosheets,with largely exposed edge sites,provide abundant catalytic active sites and allow fast charge transfer.Furthermore,they exhibit high stability for ORR and methanol tolerance.