铂、钯蜂窝催化剂高温老化对甲醇深度氧化的影响

本研究对铂、钯蜂窝催化剂及分别添加助化剂CeO_2或WO_3,并于500℃、700℃、900℃或1100℃下经受热老化4h后,考察催化剂比表面、晶相结构及其对甲醇深度氧化活性、产物分布及反应动力学网络变化的情况。实验证明,添加CeO_2后,降低了铂催化剂的耐高温性能,但对钯催化剂无明显影响。添加WO_3,降低了钯催化剂对甲醇的氧化活性。经X-线衍射分析证明,在1100℃高温下,WO_3与堇青石载体中的氧化镁和氧化钙发生强相互作用,生成了相应的钨酸盐。甲醇氧化反应动力学研究表明,甲醇在新鲜和高温热老化的铂催化剂上,反应动力学网络表示式是有区别的。     

Effects of WOx modification on the activity, adsorption and redox properties of CeO2 catalyst for NOx reduction with ammonia

A series of WO₃/CeO₂ (WOx/CeO₂) catalysts were synthesized by wet impregnation of ammonium metatungstate on a CeO₂ support. The resulting solid acid catalysts were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy (UV-Vis), Raman spectroscopy (Raman), in-situ Fourier transform infrared spectroscopy (in-situ FT-IR) of ammonia adsorption, NH₃-TPD, H₂ temperature-programmed reduction (H₂-TPR), NH₃/NO oxidation and activity measurements for NOx reduction by NH₃ (NH₃-SCR). The results show that polytungstate (WOx) species are the main species of tungsten oxide on the surface of ceria. The addition of tungsten oxide enhances the Brönsted acidity of ceria catalysts remarkably and decreases the amount of surface oxygen on ceria, with strong interaction between CeO₂ and WOx. As a result, the N₂ selectivity of NH₃ oxidation and NH₃-SCR at high temperatures (> 300℃) is enhanced. Therefore, a wide working temperature window in which NOx conversion exceeds 80% (NOx conversion > 80%) from 200 to 450℃, is achieved over 10 wt.% WOx/CeO₂ catalyst. A tentative model of the NH₃-SCR reaction route on WOx/CeO₂ catalysts is presented.     

Pt/CeO2催化氧化甲苯反应机制研究

采用浸渍法制备了Pt/CeO_2和Pt/Al2O_3催化剂,并通过XRD、BET、ICP-OES、H2-TPR、XPS等手段表征其物理化学性质.结果发现,Pt/CeO_2和Pt/Al2O_3催化剂上Pt负载量约为0.6%,Al2O_3载体上Pt颗粒尺寸更小,Pt/CeO_2的可还原性更强.甲苯催化氧化活性评价结果表明,Pt/CeO_2催化剂表现出更好的催化活性,T50=170℃,T90=190℃.通过UV-Raman、甲苯TPD、GC/MS、In-situ FTIR等手段进一步研究发现,Pt/CeO_2活化甲苯及反应供氧的机制与Pt/Al2O_3存在区别,其活性更好是因为:(1)负载在CeO_2表面存在高电子密度的Pt原子,具有更强的活化甲苯能力,可以直接使苯基和甲基间的C—C链发生断裂;(2)Pt的负载促进了CeO_2氧空位形成,进一步提高了CeO_2的储氧性能,加速氧循环.除了Pt解离气相氧之外,CeO_2还可以提供活性氧物种参与催化氧化甲苯的反应,进一步提高甲苯催化氧化效率.     

溶胶粉末复合浸渍法制备颗粒状SCR脱硝催化剂的特性

针对以V₂O₅-WO₃/TiO₂为成分的颗粒状SCR脱硝催化剂在制备过程中存在的有效组分加载均匀性等问题,尝试了利用偏钛酸溶胶作为载体的催化剂生产方法.利用粉末/溶胶复合浸渍方式设计出4种催化剂的制备方法并分别制得样品.通过在不同温度条件下样品对烟气中NO_x成分去除效能的性能测试,以及进行相关的微观表征分析,研究比较了不同制备方式对催化剂特性的影响规律,旨在探索出一种合理、高效的催化剂制备工艺.结果表明:利用偏钛酸溶胶作为载体,同步浸渍加载WO₃和V₂O₅ 2种组分,相比传统的粉末浸渍和两步浸渍方式,该方法能够使浸渍组分在载体表面获得较高的覆盖率,并有效避免了浸渍组分溶出和重结晶现象的发生,所制得的催化剂样品具有较高的脱硝效率.      

Mechanism of Hg oxidation in the presence of HCl over a commercial V2O5–WO3/TiO2 SCR catalyst

Experiments were conducted in a fixed-bed reactor containing a commercial V₂O₅/WO₃/TiO₂ catalyst to investigate mercury oxidation in the presence of HCl and O₂. Mercury oxidation was improved significantly in the presence of HCl and O₂, and the Hg⁰ oxidation efficiencies decreased slowly as the temperature increased from 200 to 400°C. Upon pretreatment with HCl and O₂ at 350°C, the catalyst demonstrated higher catalytic activity for Hg⁰ oxidation. Notably, the effect of pretreatment with HCl alone was not obvious. For the catalyst treated with HCl and O₂, better performance was observed with lower reaction temperatures. The results showed that both HCl and Hg⁰ were first adsorbed onto the catalyst and then reacted with O₂ following its adsorption, which indicates that the oxidation of Hg⁰ over the commercial catalyst followed the Langmuir–Hinshelwood mechanism. Several characterization techniques, including Hg⁰ temperature-programmed desorption (Hg-TPD) and X-ray photoelectron spectroscopy (XPS), were employed in this work. Hg-TPD profiles showed that weakly adsorbed mercury species were converted to strongly bound species in the presence of HCl and O₂. XPS patterns indicated that new chemisorbed oxygen species were formed by the adsorption of HCl, which consequently facilitated the oxidation of mercury.     

N/Ce doped graphene supported Pt nanoparticles for the catalytic oxidation of formaldehyde at room temperature

Pt catalysts with nitrogen-doped graphene oxide (GO) as support and CeO₂ as promoter were prepared by impregnation method,and their catalytic oxidation of formaldehyde (HCHO) at room temperature was tested.The Pt-CeO₂/N-rGO (reduced GO) with a mass fraction of 0.7% Pt and 0.8%CeO₂ exhibited an excellent catalytic performance with the 100% conversion of HCHO at room temperature.Physicochemical characterization demonstrated that nitrogendoping greatly increased the...     

Effect of TiO2 calcination temperature on the photocatalytic oxidation of gaseous NH3

Carbon-modified titanium dioxide(TiO2) was prepared by a sol-gel method using tetrabutyl titanate as precursor, with calcination at various temperatures, and tested for the photocatalytic oxidation(PCO) of gaseous NH3 under visible and UV light. The test results showed that no samples had visible light activity, while the TiO2 calcined at 400℃ had the best UV light activity among the series of catalysts, and was even much better than the commercial catalyst P25. The catalysts were then characterized by X-ray diffractometry, Brunauer-Emmett-Teller adsorption analysis, Raman spectroscopy, thermogravimetry/differential scanning calorimetry coupled with mass spectrometry, ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy. It was shown that the carbon species residuals on the catalyst surfaces induced the visible light adsorption of the samples calcined in the low temperature range( 300℃). However, the surface acid sites played a determining role in the PCO of NH3 under visible and UV light over the series of catalysts. Although the samples calcined at low temperatures had very high SSA, good crystallinity, strong visible light absorption and also low PL emission intensity, they showed very low PCO activity due to their very low number of acid sites for NH3 adsorption and activation. The TiO2 sample calcined at 400℃ contained the highest number of acid sites among the series of catalysts, therefore showing the highest performance for the PCO of NH3 under UV light.     

Role of NO in Hg oxidation over a commercial selective catalytic reduction catalyst V2O5–WO3/TiO2

Experiments were conducted in a fixed-bed reactor that contained a commercial catalyst, V₂O₅–WO₃/TiO₂, to investigate mercury oxidation in the presence of NO and O₂. Mercury oxidation was improved by NO, and the efficiency was increased by simultaneously adding NO and O₂. With NO and O₂ pretreatment at 350°C, the catalyst exhibited higher catalytic activity for Hg⁰ oxidation, whereas NO pretreatment did not exert a noticeable effect. Decreasing the reaction temperature boosted the performance of the catalyst treated with NO and O₂. Although NO promoted Hg⁰ oxidation at the very beginning, excessive NO counteracted this effect. The results show that NO plays different roles in Hg⁰ oxidation; NO in the gaseous phase may directly react with the adsorbed Hg⁰, but excessive NO hinders Hg⁰ adsorption. The adsorbed NO was converted into active nitrogen species (e.g., NO₂) with oxygen, which facilitated the adsorption and oxidation of Hg⁰. Hg⁰ was oxidized by NO mainly by the Eley–Rideal mechanism. The Hg⁰ temperature-programmed desorption experiment showed that weakly adsorbed mercury species were converted to strongly bound ones in the presence of NO and O₂.     

光催化氧化法处理染料中间体H酸水溶液

为了去除水中难氧化的有害染料中间体Ｈ酸,研究以ＴＩＯ２、ＺｎＯ、ＣｄＳ和Ｆｅ２Ｏ３为催化剂,采用低压汞灯为光源,对Ｈ酸水溶液进行光催化氧化实验．结果表明：ＴｉＯ２和ＣｄＳ的催化效果最好．采用ＴｉＯ２作催化剂,光催化氧化５ｈ后,Ｈ酸分解率可达９０％,反应速率遵从Ｌａｎｇｍｕｉｒ－Ｈｉｎｓｈｅｌｗｏｏｄ方程,Ｋ＝１２．３Ｌ／ｍｍｏｌ,ｋ＝２５．２×１０－６ｍｏｌ／ｈ．溶液中投加１０ｍｇ／Ｌ的Ｆｅ３＋或Ａｇ＋,可使反应时间缩短２—３ｈ．研究探讨了ｐＨ、ＴｉＯ２投加量和Ｈ酸浓度对催化氧化过程的影响．     

SO2对Mn-Cu-Ce/TiO2低温选择催化还原NO的影响

研究了SO2对Mn-Cu-Ce/TiO2选择催化还原 NO 的影响,并采用傅立叶变换红外光谱、x射线衍射光谱及暂态响应技术对Mn-Cu-Ce/TiO2催化剂的SO2中毒机理进行了探讨.结果表明,SO2 可强吸附在Mn-Cu-Ce/TiO2表面的 CuO 活性位上.并生成 CuSO4,由于 CuSO4 在低温时对SCR 反应有抑制作用,因而,催化剂的活性下降;暂态响应实验结果表明,Mn-Cu-Ce/TiO2催化剂上的SCR反应主要遵循 Langmuir-Hinshelwood机理.通过对催化剂进行硫酸化或 NO 预吸附,可以消除SO2对 Mn-Cu-Ce/TiO2的毒害作用.     

Preparation of birnessite-supported Pt nanoparticles and their application in catalytic oxidation of formaldehyde

Flaky and nanospherical birnessite and birnessite-supported Pt catalysts were successfully prepared and characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and N₂ adsorption-desorption. Effects of the birnessite morphology and Pt reduction method on the catalytic activity for the complete oxidation of formaldehyde (HCHO) were investigated. It was found that flaky birnessite exhibited higher catalytic activity than nanospherical birnessite. The promoting effect of Pt on the birnessite catalyst indicated that the reduction method of the Pt precursor greatly influenced the catalytic performance. Flaky birnessite-supported Pt nanoparticles reduced by KBH₄ showed the highest catalytic activity and could completely oxidize HCHO into CO₂ and H₂O at 50℃, whereas the sample reduced using H₂-plasma showed lower activity for HCHO oxidation. The differences in catalytic activity of these materials were jointly attributed to the effects of pore structure, surface active sites exposed to HCHO and the dispersion of Pt nanoparticles.     

Catalyst for NOx removal in nitric-acid plant gaseous effluents

The behaviour of a V₂O₅WO₃TiO₂ phosphorated catalyst, in the Selective Catalytic Reduction (SCR) of equimolar NO + NO₂ mixtures, is studied in order to analyse the possibility of its industrial utilization for the treatment of nitric-acid plant stack gases. With this new catalyst, an NO_x conversion higher than 90% molar can be achieved, the ammonia concentration at the exit gas being lower than that required to form ammonium salts, throughout the temperature range of commercial interest: 250–450°C, at a relatively high space velocity (GHSV ⩽ 40000 h⁻¹ NC). The effect of several operating variables such as oxygen concentration and NO₂/NO molar ratio in the feed is also discussed.     

Activity and hydrothermal stability of CeO2–ZrO2–WO3 for the selective catalytic reduction of NOx with NH3

A series of CeO_2–ZrO_2–WO_3(CZW)catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction(SCR)of NO with NH_3 over a wide temperature of 150–550°C.The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H_2O.The fresh catalyst showed above 90% NO_x conversion at 201–459°C,which is applicable to diesel exhaust NO_x purification(200–440°C).The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures(below 300°C),while the activity was notably enhanced at high temperature(above 450°C).The aged CZW catalyst(hydrothermal aging at 700°C for 8 hr)showed almost 80% NO_x conversion at 229–550°C,while the V_2O_5–WO_3/TiO_2 catalyst presented above 80% NO_x conversion at 308–370°C.The effect of structural changes,acidity,and redox properties of CZW on the SCR activity was investigated.The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO_2–ZrO_2 solid solution,amorphous WO_3 phase and optimal acidity.In addition,the formation of WO_3 clusters increased in size as the hydrothermal aging temperature increased,resulting in the collapse of structure,which could further affect the acidity and redox properties.     

Promotional effect of Si-doped V2O5/TiO2 for selective catalytic reduction of NOx by NH3

TiO2 supports doped with different amounts of Si were prepared by a sol-gel method, and 1 wt% vanadia (V2O5) loaded on Si-doped TiO2 was obtained by an impregnation method. The mole ratio of Si/Ti was 0.2, NOx conversion exceeds 94% at 300℃ and GHSV of 41,324 hr-1 , which is about 20% higher than pure V2O5/TiO2 . The catalysts were characterized by XRD, BET, TEM, FT-IR, NH3-TPD, XPS, H2-TPR, Raman and in situ DRIFTS. The results of FT-IR and XPS indicated that Si was doped into the TiO2 lattice successfully and a solid solution was obtained. V2O5 active component could be dispersed well on the support with the increasing of surface area of the catalyst, which was confirmed by Raman and XRD results. Above all, the numbers of acid sites (especially the Br nsted-acid) and oxidation properties were enhanced for Si-doped V2O5/TiO2 catalysts, which improved the deNOx catalytic activity.     

Photocatalytic decomposition of acrylonitrile with N–F codoped TiO2/SiO2 under simulant solar light irradiation

The solid acid catalyst, N–F codoped TiO₂/SiO₂ composite oxide was prepared by a sol–gel method using NH₄F as nitrogen and fluorine source. The prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–Visible diffuse reflectance spectroscopy (UV–Vis), ammonia adsorption and temperature-programmed desorption (NH₃-TPD), in situ Fourier transform infrared spectroscopy (FT-IR) and N₂ physical adsorption isotherm. The photocatalytic activity of the catalyst for acrylonitrile degradation was investigated under simulant solar irradiation. The results showed that strong Lewis and Brønsted acid sites appear on the surface of the sample after N–F doping. Systematic investigation showed that the highest photocatalytic activity for acrylonitrile degradation was obtained for samples calcined at 450°C with molar ratio (NH₄F to Ti) of 0.8. The degradation ratio of 71.5% was achieved with the prepared catalyst after 6-min irradiation, demonstrating the effectiveness of photocatalytic degradation of acrylonitrile with N–F codoped TiO₂/SiO₂ composite oxide. The photocatalyst is promising for application under solar light irradiation. Moreover, the intermediates generated after irradiation were verified by gas chromatography–mass spectrometry (GC–MS) analysis and UV–Vis spectroscopy to be simple organic acids with lower toxicity, and the degradation pathway was also proposed for acrylonitrile degradation with the prepared catalyst.     

Effect of phosphate on heterogeneous Fenton oxidation of catechol by nano-Fe3O4: Inhibitor or stabilizer?

The effect of phosphate on adsorption and oxidation of catechol, 1,2-dihydroxybenzene, in a heterogeneous Fenton system was investigated. In situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was used to monitor the surface speciation at the nano-Fe₃O₄ catalyst surface. The presence of phosphate decreased the removal rate of catechol and the abatement of dissolved organic compounds, as well as the decomposition of H₂O₂. This effect of phosphate was mainly due to its strong reaction with surface sites on the iron oxide catalyst. At neutral and acid pH, phosphate could displace the adsorbed catechol from the surface of catalyst and also could compete for surface sites with H₂O₂. In situ IR spectra indicated the formation of iron phosphate precipitation at the catalyst surface. The iron phosphate surface species may affect the amount of iron atoms taking part in the catalytic decomposition of H₂O₂ and formation of hydroxyl radicals, and inhibit the catalytic ability of Fe₃O₄ catalyst. Therefore, phosphate ions worked as stabilizer and inhibitor in a heterogeneous Fenton reaction at the same time, in effect leading to an increase in oxidation efficiency in this study. However, before use of phosphate as pH buffer or H₂O₂ stabilizer in a heterogeneous Fenton system, the possible inhibitory effect of phosphate on the actual removal of organic pollutants should be fully considered.     

Layered sphere-shaped TiO2 capped with gold nanoparticles on structural defects and their catalysis of formaldehyde oxidation

We describe here a one-step method for the synthesis of Au/TiO₂ nanosphere materials, which were formed by layered deposition of multiple anatase TiO₂ nanosheets. The Au nanoparticles were stabilized by structural defects in each TiO₂ nanosheet, including crystal steps and edges, thereby fixing the Au–TiO₂ perimeter interface. Reactant transfer occurred along the gaps between these TiO₂ nanosheet layers and in contact with catalytically active sites at the Au–TiO₂ interface. The doped Au induced the formation of oxygen vacancies in the Au–TiO₂ interface. Such vacancies are essential for generating active oxygen species (*O⁻) on the TiO₂ surface and Ti^3 + ions in bulk TiO₂. These ions can then form Ti^3 +–O⁻–Ti^4 + species, which are known to enhance the catalytic activity of formaldehyde (HCHO) oxidation. These studies on structural and oxygen vacancy defects in Au/TiO₂ samples provide a theoretical foundation for the catalytic mechanism of HCHO oxidation on oxide-supported Au materials.     

Effect of chromium oxide as active site over TiO2-PILC for selective catalytic oxidation of NO

This study introduced TiO2-pillared clays （TiO2-PILC） as a support for the catalytic oxidation of NO and analyzed the performance of chromium oxides as the active site of the oxidation process. Cr-based catalysts were prepared by a wet impregnation method. It was found that the 10 wt.% chromium doping on the support achieved the best catalytic activity. At 350℃, the NO conversion was 61% under conditions of GHSV = 23600 hr^-l. The BET data showed that the support particles had a mesoporous structure. Hz-TPR showed that Cr（10）TiP （10 wt.% Cr doping on TiO2-PILC） clearly exhibited a smooth single peak. EPR and XPS were used to elucidate the oxidation process. During the NO ＋ O2 adsorption, the intensity of evolution of superoxide ions （O2^-） increased. The content of Cr^3＋ on the surface of the used catalyst was 40.37%, but when the used catalyst continued adsorbing NO, the Cr^3＋ increased to 50.28%. Additionally, Oα/Oβ increased markedly through the oxidation process. The NO conversion decreased when SO2 was added into the system, but when the SO2 was removed, the catalytic activity recovered almost up to the initial level. FT-IR spectra did not show a distinct characteristic peak of SO4^2-.     

CuO对贵金属/CeO2/Al2O3催化剂的作用

制备含少量贵金属Ｐｔ、Ｐｄ的不同Ｃｕ和Ｃｅ摩尔含量比（０：１０,１：９,２：８）的催化剂,实验条件十加入ＣｕＯ可以提高Ｐｔ催化剂的二效活性;加入Ｃｕ：Ｃｅ＝２：８的ＣｕＯ降低了Ｐｄ催化剂的顾效性能,然而Ｃｕ：Ｃｅ＝１：９时可以改善Ｐｄ催化剂的三效催化性能。通过结构分析,认为ＣｕＯ的存在可以提高ｄ催化剂的比表面积,ＰｄＯ的分散度。     

Characterization and performance of Pt/SBA-15 for low-temperature SCR of NO by C3H6

Pt supported on mesoporous silica SBA-15 was investigated as a catalyst for low temperature selective catalytic reduction(SCR) of NO by C 3 H 6 in the presence of excess oxygen.The prepared catalysts were characterized by means of XRD,BET surface area,TEM,NO-TPD,NO/C 3 H 6-TPO,NH 3-TPD,XPS and 27 Al MAS NMR.The effects of Pt loading amount,O 2 /C 3 H 6 concentration,and incorporation of Al into SBA-15 have been studied.It was found that the removal efficiency increased significantly after Pt loading,but an optimal loading amount was observed.In particular,under an atmosphere of 150 ppm NO,150 ppm C 3 H 6,and 18 vol.% O 2,0.5% Pt/SBA-15 showed remarkably high catalytic performance giving 80.1% NOx reduction and 87.04% C 3 H 6 conversion simultaneously at 140°C.The enhanced SCR activity of Pt/SBA-15 is associated with its outstanding oxidation activities of NO to NO 2 and C 3 H 6 to CO 2 in low temperature range.The research results also suggested that higher concentration of O 2 and higher concentration of C 3 H 6 favored NO removal.The incorporation of Al into SBA-15 improved catalytic performance,which could be ascribed to the enhancement of catalyst surface acidity caused by tetrahedrally coordinated AlO 4.Moreover,the catalysts could be easily reused and possessed good stability.