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1.
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V 2O 5/Al 2O 3 catalysts was investigated. The Pd/V 2O 5/Al 2O 3 catalysts were more active than V 2O 5/Al 2O 3 and Pd/Al 2O 3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V 4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
2.
Methane combustion over Pd/Al 2O 3 catalysts with and without added Pt and CeO 2 in both oxygen-rich and methane-rich mixtures at temperatures in the range 250–520°C has been investigated using a temperature-programmed reaction procedure with on-line gas analysis (FTIR). During the temperature loop under oxygen-rich conditions, there was an appreciable hysteresis in the activity of unmodified Pd/Al 2O 3, which was greatly enhanced over Pd–Pt/Al 2O 3. Over both catalysts the hysteresis was reversed under slightly methane-rich atmospheres, and as temperature was reduced, a sudden collapse or fluctuations in activity were shown respectively over Pd–Pt/Al 2O 3 and Pd/Al 2O 3. Such non-steady behaviour was almost eliminated over Pd/Al 2O 3–CeO 2. Under a very narrow range of conditions and over a Pd/Al 2O 3 packed bed, oscillation of methane combustion was observed. 相似文献
3.
采用Pd/C催化剂,选择不同的溶剂体系,首先分别比较了有机碱Et 3N以及无机强碱NaOH对Pd/C催化2,4-二氯苯酚(2,4-DCP)加氢脱氯反应的影响。结果表明,醇类溶剂中,Et 3N作为质子吸收剂,2,4-DCP能够在Pd/C催化下高效彻底加氢脱氯。并通过SEM、XRD和XPS等表征分析,发现Et 3N能够中和加氢反应产生的HCl,生成三乙胺盐酸盐(Et 3N·HCl),从而消除HCl对催化剂的毒化作用,同时避免了因Et 3N·HCl在催化剂表面的沉积而引发的催化剂失活的问题。进一步研究了不同类型的有机胺对甲醇中Pd/C催化2,4-DCP加氢脱氯反应速率和反应选择性的影响。研究表明,短链有机胺(伯胺、仲胺和叔胺)更有利于Pd/C催化2,4-DCP加氢脱氯反应的进行。在此基础上建立一种新型Pd/C-甲醇-短链有机胺催化体系,可以高效、彻底地实现对多氯代苯酚类污染物的加氢脱氯降解,为实现温和条件下高浓度多氯代苯酚类污染物的环境友好无害化处理提供新的思路和方法。 相似文献
4.
通过浸渍法制备了Al_2O_3负载的Pd和Pt催化剂,考察催化剂的甲烷、乙烷和丙烷催化燃烧活性,以及助剂Ba对催化性能的影响。对于Pd/Al_2O_3催化剂,加入Ba使活性物种PdO颗粒变大和还原温度升高,形成更稳定的PdO活性物种,是Pd-Ba/Al_2O_3催化剂活性提升的主要原因。对于Pt/Al_2O_3催化剂,加入Ba助剂使活性物种Pt0含量降低,PtO_x与Al_2O_3载体相互作用增强,使PtO_x物种更难被还原为Pt~0,导致Pt-Ba/Al_2O_3催化剂活性降低。Pd和Pt催化剂催化烷烃氧化反应活性规律一致:丙烷乙烷甲烷。Pd/Al_2O_3催化剂有利于C—H键活化,Pt/Al_2O_3催化剂有利于C—C键活化。Pt/Al_2O_3催化剂对C1-C3烷烃氧化活性的差别明显大于Pd/Al_2O_3催化剂。Pt/Al_2O_3催化剂对碳比例高的烷烃活性更高。 相似文献
5.
采用HCl+H 2O 2混合溶液浸泡废旧催化剂Pd/α-Al 2O 3,滤掉氧化铝球颗粒,加入氨水沉淀滤液中Pd之外的微量杂质并过滤,在滤液中加入丁基钠黄药,形成Pd化合物沉淀,过滤,100 ℃烘干,350 ℃焙烧,生成PdO,纯度99.541%,再用H 2或CO在≥700 ℃下还原,得到纯Pd。该方法成本低,相对于王水法更环保、高效,Pd回收率>99.99%。 相似文献
6.
A series of Pd/Al 2O 3 catalysts with a wide range of mean Pd particle sizes (ca. 2–30 nm in diameter) was prepared by using various precursors (H 2PdCl 4, Pd(NO 3) 2 and Pd(AcAc) 2) and pre-treatments. The mean particle size of reduced samples was determined by H 2 chemisorption. The catalytic activity in methane oxidation under lean burn conditions was measured. The oxidation of reduced samples was studied at 300 °C. The extent of oxidation was found to decrease with increasing mean particle size. While small particles (<5 nm) oxidised very rapidly, the oxidation of large particles (ca. >15 nm) proceeded via a two-step process, being first fast and then slow. The decomposition of oxide species was studied by temperature-programmed experiments under vacuum. Two distinct oxidised species with different stability were evidenced depending on the particle size. Oxidised species in larger particles were found of lower stability than in smaller ones. A correlation between the existence of distinct types of oxide species and catalytic properties in methane oxidation was discussed. 相似文献
7.
Conversion of CCl 2F 2 in the presence (hydrogenolysis) and absence of hydrogen was investigated on Al 2O 3, AlF 3 and Pd/Al 2O 3 xerogel and aerogel catalysts. CCl 2F 2 was found to form CClF 3 and CCl 3F on Al 2O 3 and AlF 3 in the presence and absence of hydrogen as well as on the Pd/Al 2O 3 catalysts in the absence of hydrogen. Overall activity increased during the hydrogenolysis reactions at 230°C as a function of time which was paralleled by a significant increase in the yield of CClF 3 formed through a Cl/F-exchange reaction. X-ray diffraction patterns of the spent catalyst recovered after 3 h of hydrogenolysis confirmed the presence of Pd(C) (Pd–carbon solid solution) and AlF 3 phases on Pd/Al 2O 3 catalysts indicated that the carbon incorporation into the Pd lattice and the transformation of Al 2O 3 to AlF 3 starts at the initial stage of the reaction. It was concluded that AlF 3 is responsible for the Cl/F-exchange reactions. CH 4, a complete hydrogenation product, is formed during hydrogenolysis. Another route for its formation is the reaction between hydrogen in the gas phase and the interstitial carbon. 相似文献
8.
Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO 2/Al 2O 3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO 3) 2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO 2 is highly dispersed on the surface of Al 2O 3 up to 10 wt.% ZrO 2, beyond this value tetragonal ZrO 2 is formed. The presence of a small amount of ZrO 2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO 2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO 2, but it does not accelerate the activity of 0.2% Pd/ZrO 2/Al 2O 3 for methane combustion. 0.2% Pd/ZrO 2/Al 2O 3 dried at 120 °C shows highest activity for CH 4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH 4 combustion. 相似文献
9.
The reduction of NO x by hydrogen under lean burn conditions over Pt/Al 2O 3 is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al 2O 3. In this case, although pure H 2 and pure CO are ineffective for NO x reduction under lean burn conditions, H 2/CO mixtures are very effective. With a realistic (1:3) H 2:CO ratio, typical of actual exhaust gas, Pd/Al 2O 3 is significantly more active than Pt/Al 2O 3, delivering 45% NO x conversion at 160 °C, compared to >15% for Pt/Al 2O 3 under identical conditions. The nature of the support is also critically important, with Pd/Al 2O 3 being much more active than Pd/SiO 2. Possible mechanisms for the improved performance of Pd/Al 2O 3 in the presence of H 2+CO are discussed. 相似文献
10.
采用等体积浸渍法和还原法结合制备了Pd/Al2 O3催化剂,通过N2吸附-脱附、SEM、TEM、X射线衍射、X射线光电子能谱和CO原位漫反射傅里叶变换红外光谱等表征手段对制备的样品微观结构进行了系统分析,考察了不同Pd负载量和测试条件下CO催化氧化性能.实验结果表明,水合肼还原法实现了Pd在Al2 O3载体上的均匀分散... 相似文献
11.
The reduction of NO under cyclic “lean”/“rich” conditions was examined over two model 1 wt.% Pt/20 wt.% BaO/Al 2O 3 and 1 wt.% Pd/20 wt.% BaO/Al 2O 3 NO x storage reduction (NSR) catalysts. At temperatures between 250 and 350 °C, the Pd/BaO/Al 2O 3 catalyst exhibits higher overall NO x reduction activity. Limited amounts of N 2O were formed over both catalysts. Identical cyclic studies conducted with non-BaO-containing 1 wt.% Pt/Al 2O 3 and Pd/Al 2O 3 catalysts demonstrate that under these conditions Pd exhibits a higher activity for the oxidation of both propylene and NO. Furthermore, in situ FTIR studies conducted under identical conditions suggest the formation of higher amounts of surface nitrite species on Pd/BaO/Al 2O 3. The IR results indicate that this species is substantially more active towards reaction with propylene. Moreover, its formation and reduction appear to represent the main pathway for the storage and reduction of NO under the conditions examined. Consequently, the higher activity of Pd can be attributed to its higher oxidation activity, leading both to a higher storage capacity ( i.e., higher concentration of surface nitrites under “lean” conditions) and a higher reduction activity ( i.e., higher concentration of partially oxidized active propylene species under “rich” conditions). The performance of Pt and Pd is nearly identical at temperatures above 375 °C. 相似文献
12.
The role of La 2O 3 loading in Pd/Al 2O 3-La 2O 3 prepared by sol–gel on the catalytic properties in the NO reduction with H 2 was studied. The catalysts were characterized by N 2 physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO. The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La2O3 inclusion. The selectivity depends on the NO/H2 molar ratio (GHSV = 72,000 h−1) and the extent of interaction between Pd and La2O3. At NO/H2 = 0.5, the catalysts show high N2 selectivity (60–75%) at temperatures lower than 250 °C. For NO/H2 = 1, the N2 selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H2O vapor. The high N2 selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdOx phase interacting with La2O3. The formation of this phase is favored by the spreading of PdO promoted by La2O3. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al2O3 the O2 uptake is consistent with the oxidation of PdO to PdO2, and when La2O3 is present the O2 uptake exceeds that amount (1.5 times). La2O3 in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N2. 相似文献
13.
The effect of Pd on a Cu/ZnO/A1 2O 3 catalyst for methanol synthesis from CO 2/H 2 has been investigated. Activities of impregnated catalysts and physical mixtures were studied in an internal recycle reactor under 5 MPa, 250°C and a range of conversions. In all cases, the promotion of methanol production was greater at higher flow rates (lower conversions). The promotion achieved by use of Pd/A1 2O 3+ Cu/ZnO/Al 2O 3 physical mixtures was found to increase with Pd content. Greater promotion was observed over the Pd impregnated Cu/ZnO/Al 2O 3 catalysts, although this was insensitive to the particular Pd loadings used. The results are consistent with the proposal that hydrogen spillover is responsible for the observed promotion. The effectiveness of Pd as a promoter for the reduction of CuO in the catalysts was studied by TPR and was found to be related to the level of promotion in methanol production. 相似文献
14.
The effect of the Pd addition method into the fresh Pd/(OSC + Al 2O 3) and (Pd + OSC)/Al 2O 3 catalysts (OSC material = Ce xZr 1−xO 2 mixed oxides) was investigated in this study. The CO + NO and CO + NO + O 2 model reactions were studied over fresh and aged catalysts. The differences in the fresh catalysts were insignificant compared to the aged catalysts. During the CO + NO reaction, only small differences were observed in the behaviour of the fresh catalysts. The light-off temperature of CO was about 20 °C lower for the fresh Pd/(OSC + Al 2O 3) catalyst than for the fresh (Pd + OSC)/Al 2O 3 catalyst during the CO + NO + O 2 reaction. For the aged catalysts lower NO reduction and CO oxidation activities were observed, as expected. Pd on OSC-containing alumina was more active than Pd on OSC material after the agings. The activity decline is due to a decrease in the number of active sites on the surface, which was observed as a larger Pd particle size for aged catalysts than for fresh catalysts. In addition, the oxygen storage capacity of the aged Pd/(OSC + Al 2O 3) catalyst was higher than that of the (Pd + OSC)/Al 2O 3 catalyst. 相似文献
15.
Pd and Pd–Zn alloy were supported on various supporting materials using impregnation, co-precipitation and microemulsion methods, and their catalytic performances in oxidative methanol reforming (OMR) were investigated. Pd/ZnO exhibited much higher selectivity than either Pd/Al 2O 3 or Pd/ZrO 2 in the OMR for hydrogen production. This was attributed to the presence of Pd–Zn alloy on the ZnO support. Elemental Pd on Al 2O 3 or ZrO 2 promotes methanol decomposition reaction and increases CO formation. Using a microemulsion method, a highly selective Pd/ZnO can be obtained with much lower Pd loading than that in samples prepared by co-precipitation. Modification of Al 2O 3 with ZnO produced a ZnAl 2O 4 phase, which was found to be a good support for the Pd/ZnO catalyst. Highly active and selective Pd/ZnO/ZnAl 2O 4 catalysts for the OMR reaction, containing much lower Pd loadings have been developed by impregnation of the supports with an aqueous solution of Pd(NO 3) 2 + Zn(NO 3) 2. 相似文献
16.
考察过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧活性的影响以及过渡金属负载量及循环条件对甲烷降解性能的影响,采用扫描电镜、N_2吸附-脱附以及H_2程序升温还原技术对催化剂进行表征。结果表明,过渡金属Ni的添加对催化剂在(375~475)℃下的甲烷催化燃烧活性产生影响。催化剂经多次重复使用后,催化燃烧活性提高。分析原因为经过渡金属Ni改性后,可与载体形成NiAl_2O_4尖晶石,促进活性组分形成较小晶粒,并改善活性组分分散度,提高催化剂催化活性。 相似文献
17.
Nanosized particles dispersed uniformly on Al 2O 3 particles were prepared from the decomposition of precursor Cr(CO) 6 by metal organic chemical vapor deposition (MOCVD) in a fluidized chamber. These nanosized particles consisted of Cr 2O 3, CrC 1−x, and C. A solid solution of Al 2O 3–Cr 2O 3 and an Al 2O 3–Cr 2O 3/Cr 3C 2 nanocomposite were formed when these fluidized powders were pre-sintered at 1000 and 1150 °C before hot-pressing at 1400 °C, respectively. In addition, an Al 2O 3–Cr 2O 3/Cr-carbide (Cr 3C 2 and Cr 7C 3) nanocomposite was formed when the particles were directly hot pressed at 1400 °C. The interface between Cr 3C 2 and Al 2O 3 is non-coherent, while the interface between Cr 7C 3 and Al 2O 3 is semi-coherent. 相似文献
18.
Well crystallised aluminium borate Al 18B 4O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2/g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18B 4O 33 was prepared by conventional impregnation of Pd(NO 3) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18B 4O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2O 3. Pd/Al 18B 4O 33 exhibited a much lower activity than Pd/Al 2O 3 when treated in hydrogen at 500 °C or aged in O 2/H 2O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18B 4O 33 which became as active as Pd/Al 2O 3. Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18B 4O 33. The existence of two distinct types of PdO species formed on Al 18B 4O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2. 相似文献
19.
Pd-loaded Ce 0.6Zr 0.4O 2 solid solutions supported on Al 2O 3 are investigated as catalysts for the reduction of NO by CO. The attention is focused on the role of the Ce 0.6Zr 0.4O 2 and of the Pd dispersion on the catalytic activity. The system shows a very high activity below 500 K, which is almost independent on the Pd dispersion. The high activity is attributed to a promoting effect of the Ce 0.6Zr 0.4O 2 on the NO conversion. Investigation of the influence of high temperature treatments disclosed a thermal stabilisation of both Ce 0.6Zr 0.4O 2 and Al 2O 3 in the Ce 0.6Zr 0.4O 2/Al 2O 3 system. 相似文献
20.
Alumina (Al 2O 3) is widely used in the chemical industry as the catalyst and support due to its high specific surface area, abundant pore size distribution and chemical stability. However, the occurrence of hydration in water environment, result in outstanding decrease in specific surface area and collapse of pore structure. In this work, dodecyl phosphoric acid (PA) is used to modify the surface of Al 2O 3 to obtain a series of hydrophobic material (Al 2O 3-PA). Based on XPS and NMR analysis, PA is chemically bonded on Al 2O 3 to form P-O-Al bond. Furthermore, BET and WCA results display that Al 2O 3-1PA exhibits excellent the hydrophobicity and hydrothermal stability while maintains the pore structure. Take it as the substrate to support the Pd nanoparticles, the as-prepared Pd/Al 2O 3-PA shows the superior catalytic performance in the hydrogenation of phenol and anthraquinone relative to Pd/Al 2O 3, indicating the accessibility of Pd sites after PA modification. Especially, the significantly enhanced stability is also obtained in four cycles for aqueous phenol hydrogenation. This can be ascribed that the PA modification inhibits the aggregation of Pd nanoparticles and the products adhesion in the reaction process. The extension of PA coatings to monolithic catalysts could expand their current capabilities in industrial applications and warrants ongoing investigation. 相似文献
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