TiO2 Supported Nano—Au Catalysts Prepared via Solvated Metal Atom Impregnation for Low-Temperature CO Oxidation

TiO₂ supported nano-Au catalysts were prepared by solvated metal atom impregnation (SMAI) method. The catalysts were characterized by means of AAS, TPD, H₂ reduction desorption (H₂-RD), XRD, TEM, XPS and tested for low-temperature CO oxidation. XRD and TEM results showed that the pretreatment temperature had an influence on the particle size of Au/TiO₂catalysts. The average particle size increased with the increase in pretreatment temperature. XPS indicated that gold in the catalysts was presented in the form of metallic state clusters. Catalytic studies showed these catalysts were very active and stable in low-temperature CO oxidation. The CO oxidation activity of the catalysts increased as the Au particle size decreased. The measurement results of AAS, TPD and H₂-RD revealed that there were some organic fragments on the surface of Au particles which might be responsible for the high stability of the Au/TiO₂ catalysts.     

CO Oxidation and Toluene Hydrogenation by Pt/TiO2 Catalysts Prepared from Dendrimer Encapsulated Nanoparticle Precursors

Generation 4 hydroxyl terminated polyamidoamine (PAMAM) dendrimer encapsulated nanoparticles (DENs) were examined as precursors for Pt/TiO₂ catalysts. In this preparation method, the dendrimers were initially used to template and stabilize Pt nanoparticles in solution. DENs were then deposited onto titania, and activation conditions for dendrimer thermolysis were examined. The interactions between PAMAM dendrimers and the titania were found to differ from previous reports of dendrimer-support interactions with silica, alumina, and zirconia. In the case of titania, the amide bonds were found to shift 100 cm^?1, indicating adsorption occurs primarily through amide–titania interactions. Infrared spectroscopy, CO oxidation catalysis, and toluene hydrogenation catalysis were used to evaluate protocols for removing the dendrimer. Thermal decomposition of the DENs in O₂ or CO/O₂ atmospheres led to the formation of surface isocyanates that were preferentially bound to the metal nanoparticles. CO oxidation catalysis was insensitive to the activation protocol used, and infrared spectroscopy of adsorbed CO showed only small differences in the basic surface properties of the resulting Pt catalysts. Toluene hydrogenation catalysis was more sensitive to different activation pretreatments. The most active hydrogenation catalysts resulted from short, low temperature (150 °C) hydrogen treatments while longer treatments at higher temperature (300 °C) resulted in slightly less active catalysts.     

Mesoporous Au/TiO2 Catalysts for Low Temperature CO Oxidation

The activity and stability of structurally well defined mesoporous Au/TiO₂ catalysts with different support morphologies and pore sizes for low temperature CO oxidation was investigated by kinetic measurements and in-situ IR spectroscopy. The resulting catalysts with Au particle sizes of ∼3 nm exhibit a high activity for CO oxidation, similar to or exceeding that of highly active standard Au/TiO₂ catalysts with similar size Au nanoparticles and loading, and a significantly lower tendency for deactivation. Possible reasons for the improved performance of these catalysts are discussed.     

TiO2 Supported Nano-Au Catalysts Prepared Via Solvated Metal Atom Impregnation for Low–Temperature CO Oxidation

The Ce _x Ti_1?x O₂ mixed oxides at different mole ratios (x=0.1–1.0) were prepared by co-precipitation of TiCl₄ and Ce(NO₃)₃. The structural and reductive properties of the Ce _x Ti_{1? x} O₂ were affected by calcination temperature. At x=0.1–0.3, CeTi₂O₆ phase was formed and mainly as amorphous after calcination at 650°C. At x=0.3, only CeTi₂O₆ was formed after calcination at 750°C and CeTi₂O₆ crystallized completely after calcination at 800°C. TPR analyses showed that the amount of H₂ consumption by Ce _x Ti_1?xO₂ (650°C) (except x=0.1) was greater than that by single CeO₂, and the valence of CeO₂was the lowest (+3.18) at x=0.3. CuO/Ce_0.3Ti_0.7O₂ was prepared by the impregnation method and catalytic properties were examined by means of a GC micro-reactor NO+CO reaction system, BET, TPR, XRD, XPS and NO-TPD. It was found that CuO/Ce_0.3Ti_0.7O₂ calcined at 650°C had the highest activity in NO+CO reaction with 100% NO conversion at reaction temperature of 300°C, and at 650°C Ce_0.3Ti_0.7O₂just began to crystallize. The catalytic activities were largely affected by the pre-treatment conditions. At low reduction temperature (100°C), CuO species was difficult to reduce. When high degree of reductions took place, both CuO species and Ce_0.3Ti_0.7O₂ reduced and thus a part of CuO species on the support surface would be covered. The XPS and NO-TPD analyses showed that CuO/Ce_0.3Ti_0.7O₂ had four NO absorption centers (Cu⁺, Cu²⁺(I), Cu²⁺(II) and Ce³⁺). The CuO species involving in NO+CO reaction included Cu²⁺(I) and Cu⁺, and CeO₂ species (Ce³⁺ and Ce⁴⁺).     

Effect of Pretreatment on Carbon-Supported Au/TiO2 Catalysts for Preferential Oxidation of CO

The impact of thermal treatment at various preparation stages of carbon supported Au/TiO₂ catalysts prior to oxidation of CO in the presence and absence of hydrogen was studied. An increase in catalytic activity for thermally treated samples due to a more ordered structure of TiO₂ was observed. A reversible deactivation of the catalysts occurred in the absence of hydrogen. However, the activity was restored at preferential CO oxidation conditions in presence of hydrogen.     

制备参数对Au/TiO_2催化剂上CO低温氧化性能的影响

以溶胶-凝胶法制备TiO2载体,用沉积-沉淀法制备出一系列负载型Au/TiO2。系统考察了焙烧温度、金的负载量、反应液pH值、沉淀剂种类以及Cl-存在与否等制备参数对催化剂活性的影响。以室温下CO的催化氧化为探针反应,确定催化剂的最适宜制备参数,并对优化的质量分数为1.0%的Au/TiO2催化剂进行了活性稳定性测试。结果表明：Au/TiO2的最适宜焙烧温度是200～350℃;反应液的最适宜pH值为9;最适宜沉淀剂是NaOH;金的负载量（质量分数,下同）在0.5%～5.0%范围内时,金含量越高,催化剂活性和热稳定性越好。大量Cl-的存在能导致催化剂活性的显著下降。对优化的Au/TiO2催化剂在室温下催化氧化不同浓度的CO进行循环测试,经历3次循环,连续反应2 160 min后,CO的转化率仍为100%。     

The Effects of Water on CO Oxidation over TiO2 Supported Au Catalysts

Polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) was used to investigate the effects of water on CO oxidation catalyzed by TiO₂ supported Au. The introduction of water into the reactant mixture caused two effects: (1) a decrease in the CO coverage; and (2) the appearance of a carbonate species. Since both effects inhibit CO oxidation, the promotional effects of water found by previous researchers can only be rationalized by its effects on molecular oxygen adsorption and activation. Although this argument is not confirmed by the PM-IRAS data alone, this conclusion is consistent with previous studies. It is further inferred from this study that carbonate species first form on TiO₂ sites and then migrate to Au sites. Surface hydroxyl species may play the same promotional role as adsorbed water.     

Ag／TiO2光催化氧化还原反应脱除水体中无机氮

采用光催化还原法制备了高活性的载银二氧化钛光催化剂，并用XRF、TEM、XRD及XPS、UV-Vis方法对催化剂进行了表征．考察了负载舨的含量、催化剂制备时间、搅拌气体的种类以及Fe^2＋的添加等条件对该催化剂光催化水体脱氮活性的影响．结果表明：载银量1．0％时去除效果最佳；制备催化剂时光照时间不充分会使催化剂失去还原效力；氮气保护下催化剂反应活性更高；Fe^2＋的加入利于光催化反应；2h光催化含氨氮和亚硝基氮的水样。总脱氮率达到了63．9％．     

纳米Ag/TiO2复合材料的抗菌性能

采用Sol gel法制备掺杂不同质量分数银的纳米Ag/TiO2复合材料,研究了其对抗菌性能的影响。结果表明,银掺杂后的复合材料和应用其整理的纺织品不需紫外光照射就具有较强的抗菌性能,对大肠杆菌和金黄葡萄球菌的透明抑菌圈达到13～17mm。复合材料中银的掺杂能抑制粒径的长大,促进TiO2从锐钛型向金红石相的转移,但其质量分数对复合材料的抗菌性能影响不大。n(Ti)∶n(Ag)=20∶1时,复合材料的抗菌性能最佳,透明抑菌圈达到17mm。     

CO Spillover and Oxidation on Pt/TiO2

The adsorption of CO has been measured on a 2.5 wt% Pt/TiO₂ catalyst using TPD. A somewhat surprising observation is that (i) CO₂ is produced, even though oxygen is not dosed into the system, (ii) repeated experiments result in the same amount of CO₂ desorption. The results appear to be due to a combination of factors–(i) is due to spillover of CO from the Pt to the TiO₂ support, while (ii) is due to the diffusion of Ti³⁺ into the bulk of the TiO₂ crystallite, which effectively removes the surface non-stoichiometry which might otherwise be expected.     

Highly Active Au/TiO2 Catalysts for Low-Temperature CO Oxidation: Preparation, Conditioning and Stability

Using a modified depositionprecipitation procedure and a new reductive conditioning method, Au/TiO₂ catalysts with small metallic Au particles (<2 nm) and a very high activity for low-temperature CO oxidation were prepared. The particles are stable during reaction; a decreasing activity is caused by the accumulation of by-products on the catalyst.     

光催化还原法制备载Ag光催化剂

采用光催化还原法在大颗粒负载型TiO2表面上制备了负载型Ag/TiO2光催化剂。以对甲基橙溶液的降解活性为研究对象,考察了光催化剂制备过程中AgNO3溶液浓度,还原反应气氛,还原反应时间,反应液pH值,EDTA的加入等反应条件的影响。研究了光催化还原法制备载Ag催化剂的可行性,得出光催化还原法的优化制备条件。     

Preservation of the Activity of Supported Gold Catalysts for CO Oxidation

Procedures leading to the preservation of activity of supported gold catalysts for CO oxidation are reviewed. The inclusion of iron as Fe(OH)₃ in preparing catalysts using tin oxide, ceria and zirconia as supports gives better activity and much improved stability with time-on-stream. In the case of Au/Fe-SnO₂ (0.5–0.9% Au), the effect is maximal with ~4% Fe. The stability of catalysts based on ceria as support is also much better when small amounts of either iron or lanthanum during preparation of the support by thermal decomposition of nitrates. Au/SnO₂ catalysts often suffer initial deactivation followed by an increase in activity with time-on-stream; a period of refrigeration (7d) induces an excellent stability at high conversion.     

直接氧化法制备TiO2-Al2TiO5复相陶瓷

以Ti—Al—C和TiC—Ti—Al体系为反应体系,采用直接氧化法制备Al2TiO3-TiO2复相陶瓷。研究了氧化温度对体系合成产物组成的影响。结果表明,两种体系的合成产物都由Al2TiO3和TiO2相组成,没有杂质相存在。碳高温氧化成CO2向外扩散,在坯体内形成疏松通道,利于O2的渗入,提高了氧化反应程度。     

The influence of Si-modified TiO2 on the activity of Ag/TiO2 in CO oxidation

Nanocrystalline TiO₂ and Si-modified TiO₂ with Si/Ti ratios 0.01, 0.05, 0.1, and 0.3 were prepared by the solvothermal method and employed as the supports for Ag/TiO₂ catalysts for CO oxidation reaction. The incorporation of Si into the TiO₂ lattice in the form of Ti–O–Si as revealed by FT-IR results could inhibit the agglomeration of TiO₂ crystallites, resulting in an increase of both surface area and metal dispersion. However, there existed an optimum content of Si/Ti at ca. 0.05–0.1 which resulted in an improved catalytic activity of Ag/TiO₂ in CO oxidation. Based on the O₂-temperature program desorption (O₂-TPD) results, the catalysts with appropriate amounts of Si/Ti exhibited higher amount of O₂ adsorption and much lower desorption temperature. It is suggested that the presence of Ti–O–Si promoted the formation of active oxygen species and increased the mobility of lattice oxygen so that the catalytic activity was enhanced. There was no improvement in CO oxidation activity of the Ag/TiO₂ catalyst when the Si/Ti was further increased to 0.3 due probably to the formation of amorphous SiO₂ instead of the Ti–O–Si bond.     

Role of Preparation Techniques in the Activity of Au/TiO2 Nanostructures Stabilised on SiO2: CO and Preferential CO Oxidation

Au colloid and titania in different sequence or Au-oxide nano ensembles preformed in hydrosol were deposited on inert amorphous silica or mesoporous SBA-15. It was compared with gold colloid adsorbed on TiO₂ or silica support. The formation of the Au/TiO₂ interface is discussed in terms of surface charges. Preferential CO oxidation in the presence of hydrogen (PROX) has been correlated with the CO oxidation activity and structural properties, perimeter and the influence of the TiO₂ morphology on the catalytic activity has been demonstrated.     

Mo掺杂V/TiO2催化2-甲基吡啶气相氧化合成2-吡啶甲醛

以XRD、H2-TPR等方法表征Mo掺杂V/TiO2新型催化剂,并详细考察了催化剂组成、反应温度、空速等对Mo掺杂V/TiO2催化2-甲基吡啶氧化合成2-吡啶甲醛的影响。实验研究结果表明,Mo的掺杂提高了催化剂的还原能力和催化活性。低反应温度和高空速可以提高对2-吡啶甲醛的选择性。钒和钼的最佳比率为2.9:1,催化剂的最佳负载量为7%。最佳反应条件下(催化剂焙烧温度600℃,反应温度290℃,10%2-甲基吡啶水溶液的流速为0.2 mL·min-1,氧气的流速为0.1 L·min-1,空速为3083 h-1),2-甲基吡啶的转化率为70.2%,2-吡啶甲醛的选择性为88.3%,与文献报道的未使用Mo掺杂的催化剂所得的结果 (转化率14%,选择性93%)相比,在选择性相差不大的情况下,转化率大幅度提高。