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Pt催化丙烷脱氢过程中结焦反应的粒径效应与Sn的作用 总被引:1,自引:0,他引:1
用乙二醇还原法制备了Pt颗粒平均粒径分别为2.0、4.6、12.1 nm的Pt/Al2O3催化剂,同时用浸渍法制备了PtSn/Al2O3双金属催化剂,并考察了各催化剂在丙烷脱氢过程中的结焦行为。分别用H2化学吸附、透射电镜、热重分析、元素分析、红外光谱、拉曼光谱等手段对催化剂进行了表征。表征结果显示,催化剂金属上的结焦速率与Pt金属颗粒粒径密切相关。具有较小Pt颗粒的催化剂金属上的结焦速率明显大于具有较大Pt颗粒的催化剂。具有较小Pt颗粒的催化剂上生成的焦含有较少的氢,其石墨化程度也较高。本研究中PtSn/Al2O3催化剂金属上的结焦速率高于Pt/Al2O3催化剂,并且在双金属上生成的焦具有更高的石墨化程度。结合Pt/Al2O3催化剂上的结焦机理,对高性能丙烷脱氢催化剂提出了新的概念设计。 相似文献
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用廉价的丙烷脱氢制丙烯是解决丙烯供应紧张问题的途径之一,研究优异性能的丙烷脱氢催化剂具有重要意义。采用分步浸渍法制备不同类型的丙烷脱氢催化剂Pt/Al2O3,在固定床反应器中考察助催化剂Sn、Ga、In和K对催化剂性能的影响。结果表明,Pt-Sn/Al2O3催化剂性能略优于Pt-Ga/Al2O3和Pt-In/Al2O3,并且比较稳定。在Pt-Sn/Al2O3催化剂中加入适量K,可有效改善催化剂性能,但高温条件下积炭严重,有待深入研究和改进。 相似文献
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采用十六烷基三甲基溴化铵(CTAB)/正丁醇/环己烷/H2PtCl6溶液的微乳体系,以N2H4·H2O为还原剂,Al2O3为载体制备Pt/Al2O3催化剂。以邻氯硝基苯(o-CNB)选择加氢反应为探针,考察微乳液组成对Pt/Al2O3催化剂选择加氢活性的影响。运用XRD、XPS、IR、TEM和EDS对载体和催化剂进行表征。结果表明,微乳体系中CTAB∶正丁醇∶环己烷质量比9∶21∶70,3.6% H2PtCl6溶液中制备的Pt/Al2O3催化剂的o-CNB选择加氢活性最高。Pt粒子粒径5 nm左右,与载体之间没有明显的电子效应。对于取代位置不同的间、对氯硝基苯(m-CNB、p-CNB)加氢,Pt/Al2O3催化剂也表现出较高的催化活性。 相似文献
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采用胶体沉积法制备不同载体(Ni2O3、Co3O4、TiO2、Al2O3)的Pt-Fe/MeOx催化剂用于甲醛室温催化氧化。活性测试表明,以γ-Al2O3为载体的Pt-Fe/Al2O3催化剂具有较高的催化活性,在25℃时甲醛的转化率可达到100%,而且Pt-Fe/ Al2O3催化剂还表现出良好的稳定性。采用各种表征技术对Pt-Fe/Al2O3的形貌、价态及氧化还原性等物理化学性质进行了研究,结果表明:Pt-Fe/Al2O3催化剂中Pt物种和Fe物种在Al2O3载体的表面上均匀分散;二者之间存在着较强的相互作用,在Al2O3载体的表面上形成一些类似Pt-O-Fe活性物种,有效促进了Pt-Fe/Al2O3催化性能,从而显示出较高的氧化活性。 相似文献
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以共沉淀-浸渍法制备了SO42-/TiO2/Al2O3型固体酸催化剂,醋酸与正丁醇酯化反应作为探针反应,考察SO42-/TiO2/Al2O3型固体酸催化剂的催化性能,采用响应面法对制备催化剂过程中的陈化温度、硫酸浸渍液浓度和焙烧温度因素进行优化,通过XRD和IR对制备的固体酸催化剂进行表征。结果表明,在陈化温度-4 ℃、硫酸浸渍液浓度1.48 moL·L-1和焙烧温度586 ℃条件下制得的催化剂催化性能最高,醋酸正丁酯酯化率可达98.1%,重复使用性良好。 相似文献
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利用NaBH4还原机制,采用经不同方法预处理的碳载体成功制备出Pt/C-HNO3、Pt/C-H2O2和Pt/C 3种碳载铂纳米催化剂.通过扫描电镜(SEM)、透射电镜(HR-TEM)、循环伏安(CV)和COad溶出技术进行表征.结果表明,所制备的催化剂大小分布较为均一,平均粒径约为4 nm;HR-TEM观察发现,Pt/C-HNO3中铂纳米粒子的表面具有较高的台阶原子密度;在COad溶出实验中Pt/C-HNO3表现出较强的抗一氧化碳毒化能力;所制备的3种催化剂及商业催化剂Pt/C JM对乙醇氧化的电催化活性顺序为:Pt/C-HNO3 > Pt/C-H2O2 > Pt/C > Pt/C JM,其中Pt/C-HNO3的电催化活性和稳定性分别为Pt/C JM的1.5倍和1.9倍. 相似文献
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采用沉淀法制备了Pt/SO42-/ZrO2-Al2O3 (PtSZA)催化剂,考察了氢氧化锆水凝胶干燥速率、锆盐浓度、铂含量、Al2O3和SO42-添加顺序等制备条件对PtSZA异构化性能,尤其是低温异构化性能的影响,并用XRD和TG对催化剂进行了表征。结果表明,提高水凝胶的干燥速率降低了PtSZA催化剂中的硫含量,大大提高了催化剂中的单斜相,进而导致了催化剂低温失活加速以及高温活性下降。较低或较高的锆盐浓度劣化了PtSZA的低温异构化稳定性,以0.4~0.6mol/L硝酸氧锆制备的催化剂硫含量和四方相氧化锆含量较高,异构化活性相对较好,Al2O3和SO42-添加顺序对PtSZA异构化性能没有明显影响。 相似文献
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以羰基铂锡化合物为前体,采用浸渍法将其负载于Zn改性Al2O3载体上制备了PtSn/xZn-Al2O3催化剂,考察了Zn的添加对催化剂丙烷脱氢性能的影响。采用N2吸附-脱附、X射线衍射(XRD)、吡啶红外吸附(Py-IR)、氨气程序升温脱附(NH3-TPD)、透射电子显微镜(TEM)等手段对催化剂的孔结构、表面酸性以及积炭行为进行了分析。结果表明,PtSn/xZn-Al2O3催化剂孔道以介孔为主,孔径集中分布于8~10nm;Zn助剂的添加,在催化剂表面会形成ZnO物种,可使PtSn/Al2O3催化剂上的金属颗粒粒径减小、分散更加均匀;Zn的加入能有效降低催化剂表面酸量,主要表现为L中强/强酸中心的降低,随着Zn含量的增加,催化剂表面酸量先减少后增加。少量Zn的存在可使PtSn/Al2O3丙烯选择性和稳定性显著提高,但过量Zn的加入会降低催化剂的脱氢活性,适宜Zn的质量分数为0.75%~1.0%。反应后催化剂表面积炭主要表现为烯烃性质和芳香烃性质,Zn的添加可有效抑制积炭的形成,提高催化剂稳定性。 相似文献
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通过等体积浸渍法制备单贵金属Pt/γ-Al2O3和双金属Pt-Ce/γ-Al2O3催化剂,考察Ce对催化剂活性的影响,确定催化剂最优配比。结果表明,当Pt的负载量为质量分数0.5%时,Pt/γ-Al2O3催化活性最高;当Pt的负载量为质量分数0.2%,Ce的负载量为质量分数1.0%时,Pt-Ce/γ-Al2O3催化剂的催化活性最高。Pt-Ce/γ-Al2O3催化剂的甲苯转化率高于Pt/γ-Al2O3催化剂。随着Pt负载量增大,催化剂孔容、孔径减小。粉体式催化剂性能优于整体式催化剂,但差别不大;Ce的添加有助于催化剂活性的提升。 相似文献
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以碱共沉淀法制备Mg-Al水滑石,然后采用浸渍法负载活性组分Pt,经焙烧、氢气还原得到Pt/Al_2O_3与Pt/Mg O-Al_2O_3催化剂,采用XRD、N2吸附-脱附、FT-IR、H2-TPR和Py-IR等分析Mg O的加入对Pt/Al_2O_3催化剂结构性能的影响,并在甲基环己烷连续脱氢反应中对比两种催化剂活性。结果表明,Pt/Mg O-Al_2O_3催化剂比表面积小于Pt/Al_2O_3催化剂,且表面基本无酸性活性中心,但表现出与Pt/Al_2O_3催化剂相同的脱氢活性。在Pt负载质量分数2%、催化剂用量0.5 g、甲基环己烷0.1 m L·min-1纯样进料和325℃反应10 h后,原料平均转化率79.9%,脱氢产物只有甲苯,对应的产氢速率192.8 mmol·(g-metal·min)-1,表现出优良的脱氢活性。 相似文献
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Kiyoshi Yamazaki Tadashi Suzuki Naoki Takahashi Kouji Yokota Masahiro Sugiura 《Applied catalysis. B, Environmental》2001,30(3-4):459-468
The NOx storage-reduction catalysis under oxidizing conditions in the presence of SO2 has been investigated on Pt/Ba/Fe/Al2O3, Pt/Ba/Co/Al2O3, Pt/Ba/Ni/Al2O3, and Pt/Ba/Cu/Al2O3 catalysts compared with Pt/Ba/Al2O3, Pt/Fe/Al2O3, Pt/Co/Al2O3, Pt/Ni/Al2O3, Pt/Cu/Al2O3 and Pt/Al2O3 catalysts. The NOx purification activity of Pt/Ba/Fe/Al2O3 catalyst was the highest of all the catalysts investigated in this paper after an aging treatment. That of the aged Pt/Ba/Co/Al2O3 and Pt/Ba/Ni/Al2O3 catalysts was essentially the same as that of the aged Pt/Ba/Al2O3 catalyst, while that of the aged Pt/Ba/Cu/Al2O3 and Pt/Cu/Al2O3 catalysts was substantially lower than the others.
The Fe-compound on the aged Pt/Ba/Fe/Al2O3 catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the Pt/Ba/Al2O3 catalyst without the Fe-compound. XRD and EDX show that the Fe-compound inhibits the growth in the size of BaSO4 particles formed on the Pt/Ba/Fe/Al2O3 catalyst under oxidizing conditions in the presence of SO2 and promotes the decomposition of BaSO4 and desorption of the sulfur compound under reducing conditions. 相似文献
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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
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Ag-based catalysts supported on various metal oxides, Al2O3, TiO2, and TiO2–Al2O3, were prepared by the sol–gel method. The effect of SO2 on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO2–Al2O3 in comparison to Ag/Al2O3 and Ag/TiO2, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO2–Al2O3. NO3− rather than NO2− or NOx reacted with the carboxylate species to form CN or NCO. NO2 was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO2–Al2O3. More amount of formate (HCOO−) and CN were generated on the Ag/TiO2–Al2O3 catalyst than the Ag/Al2O3 catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO2 oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO2–Al2O3 system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO2 toleration to the Ag/Al2O3 catalyst. 相似文献
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A mean field model, for storage and desorption of NOx in a Pt/BaO/Al2O3 catalyst is developed using data from flow reactor experiments. This relatively complex system is divided into five smaller sub-systems and the model is divided into the following steps: (i) NO oxidation on Pt/Al2O3; (ii) NO oxidation on Pt/BaO/Al2O3; (iii) NOx storage on BaO/Al2O3; (iv) NOx storage on Pt/BaO/Al2O3 with thermal regeneration and (v) NOx storage on Pt/BaO/Al2O3 with regeneration using C3H6. In this paper, we focus on the last sub-system. The kinetic model for NOx storage on Pt/BaO/Al2O3 was constructed with kinetic parameters obtained from the NO oxidation model together with a NOx storage model on BaO/Al2O3. This model was not sufficient to describe the NOx storage experiments for the Pt/BaO/Al2O3, because the NOx desorption in TPD experiments was larger for Pt/BaO/Al2O3, compared to BaO/Al2O3. The model was therefore modified by adding a reversible spill-over step. Further, the model was validated with additional experiments, which showed that NO significantly promoted desorption of NOx from Pt/BaO/Al2O3. To this NOx storage model, additional steps were added to describe the reduction by hydrocarbon in experiments with NO2 and C3H6. The main reactions for continuous reduction of NOx occurs on Pt by reactions between hydrocarbon species and NO in the model. The model is also able to describe the reduction phase, the storage and NO breakthrough peaks, observed in experiments. 相似文献
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Aisling M. OConnor Yves Schuurman Julian R.H. Ross Claude Mirodatos 《Catalysis Today》2006,115(1-4):191-198
The mechanism of the CO2 reforming of methane reaction over the Pt/ZrO2 catalyst was investigated using a temporal analysis of products (TAP) reactor system. For comparative purposes, the reaction pathway using a Pt/Al2O3 catalyst was also examined. A reaction sequence is suggested for both catalysts. Over both catalysts, methane decomposition takes place over platinum. The main difference between the two catalysts concerns the carbon dioxide dissociation. Over Pt/Al2O3 this step is assisted by hydrogen. Over Pt/ZrO2 this step takes place over the zirconia support and involves surface vacancies. Moreover, large pools of formate and carbonate species are present on the zirconia. Transient studies conducted to determine the origin of carbon species accumulated during CO2 reforming revealed that more than 99% of the carbon was derived from the methane molecule over both catalysts. Over the Pt/ZrO2 catalyst, only a single very reactive carbon species was detected, while over the Pt/Al2O3 a second less active species was also formed. 相似文献
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采用真空浸渍法制备了不同Ce含量的Pt-Sn/Ce-γ-Al2O3催化剂,采用X射线衍射、CO脉冲吸附、程序升温还原、热重及氨程序升温脱附等手段对催化剂进行表征,研究Ce助剂对Pt-Sn/Ce-γ-Al2O3催化剂结构及其催化长链烷烃(n-C16~20)临氢脱氢反应性能的影响。结果表明,Ce的引入可以调变催化剂酸性,改变催化剂的还原性能;Pt、Sn和Ce以及载体之间产生较强的相互作用能够促进氧化铂的还原,提高铂粒子的热稳定性,抑制锡物种还原,降低催化剂积炭,有利于提高催化剂的脱氢活性及稳定性。 相似文献
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Hydrodechlorination of CCl4 over Pt/Al2O3: effects of platinum particle size on product distribution
Jong Wook Bae In Gi Kim Jae Sung Lee Kyung Hee Lee Eun Joo Jang 《Applied Catalysis A: General》2003,240(1-2):129-142
The impregnated platinum catalysts showed various platinum particle sizes depending on the nature of the platinum precursors (Pt(NH3)2(NO2)2 versus H2PtCl6) and on the pH of the Al2O3 suspension. The average platinum particle size increased with decrease in pH of the suspension in case of Pt(NH3)2(NO2)2, but this trend was vice versa for H2PtCl6. The product distribution in hydrodechlorination (HDC) of CCl4 varied greatly with the platinum particle size; the larger the platinum particle size was, the higher was the selectivity to CHCl3. To elucidate the origin of this platinum particle size effect on product distribution, CO chemisorption, NH3 and CO2 temperature-programmed desorption (TPD), high resolution transmission electron microscopy (HRTEM), temperature-programmed surface reaction (TPSR), Fourier-transformed-infrared spectra (FT-IR) and X-ray absorption fine structure (XAFS) experiments were carried out. The formation of completely dechlorinated CH4 was favorable owing to the strong chemisorption of CCl4 on the small platinum particles characterized by low surface coordination numbers and by an electron-deficient property. The nature of carbonaceous species formed on platinum surface at the beginning of reaction also varied greatly with platinum particle sizes and changes of electronic state of platinum particles affected catalytic activity and products’ distribution. 相似文献
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F. Cabello Galisteo R. Mariscal M. Lpez Granados J.L.G. Fierro R.A. Daley J.A. Anderson 《Applied catalysis. B, Environmental》2005,59(3-4):227-233
The reactivation of thermally sintered Pt/Al2O3 catalysts used in the simultaneous oxidation of CO and propene has been achieved by an oxychlorination treatment. The catalyst can be considered to model the active component of the catalytic converter fitted to diesel driven cars. Platinum crystallites redispersion was verified by XRD, H2 chemisorption, TEM and FTIR. The extent of regeneration reflects the platinum particle redispersion achieved by such a treatment. Oxychlorination also introduced electronic effects in the Pt particle caused by the presence of chlorine at the Pt-Al2O3 interface but no detrimental result of this was observed in the oxidation reactions. The results indicate that the deactivation of the diesel oxidation catalysts (DOCs) can be reverted by this simple treatment resulting in a remarkable recovery of the catalytic activity. 相似文献