低负载贵金属催化剂对二甲醚催化燃烧的催化活性

采用浸渍法以g-Al2O3为载体制备了多种低负载量的Pd和Pt催化剂,在微型固定床反应器装置上进行了二甲醚(DME)催化燃烧实验. 考察了不同贵金属负载量的Pd/g-Al2O3和Pt/g-Al2O3催化剂的活性,及浸渍顺序对Pd-Pt/g-Al2O3双金属负载催化剂活性的影响,并测试了贵金属负载摩尔比不同的双金属负载催化剂的活性. Pt负载量0.025%(w)的催化剂在190℃将DME完全燃烧;Pd和Pt共同负载的催化剂[Pd:Pt=2:1(mol), Pt 0.025%(w), Pd 0.027%(w), Pt先负载]性能更好,在175℃将DME完全燃烧;200 h实验后2种催化剂活性降低均小于5%.     

Pt-Pd催化剂的萘加氢活性和抗氮性能研究

本工作研究了球形硅铝氧化物负载的铂-钯(Pt-Pd)贵金属催化剂的加氢活性和抗氮性能.首先,以过量共浸渍法制成5种不同负载量的Pt-Pd贵金属催化剂,元素分析结果表明浸渍液中Pt的质量分数升高会显著提高催化剂上Pt的负载量并明显降低Pd的负载量,而浸渍液中Pd的质量分数的升高对Pt、Pd的负载量几乎无影响;进一步的分析...     

Pd-Pt-Ce/Al_2O_3催化剂在VOC净化处理中的催化性能

采用浸渍法制备Pd-Pt-Ce/Al_2O_3催化剂,考察贵金属Pd和Pt负载量、助剂种类及负载量、空速对催化甲苯燃烧活性的影响。结果表明,适宜的贵金属负载量和助剂可极大提高Pd-Pt/Al_2O_3催化剂活性,当Pd和Pt质量分数分别为0.05%和0.005%、助剂Ce质量分数为1%时,Pd-Pt-Ce/Al_2O_3催化剂在低温条件下表现出较好的催化性能。空速对催化剂的催化活性影响较为明显,适宜的空速低于20 000 h-1。     

Ni/H-USY催化剂上甲烷选择性催化还原NOx的性能

考察了不同负载量的Ni/H-USY（ultra stable Y zeolite）催化剂在氧气含量5%情况下甲烷选择性催化还原氮氧化物性能,同时考察了添加微量Pd和Pt对15％(质量分数)Ni催化剂性能的影响.结果表明,催化剂的催化活性与活性组分的含量间存在密切关系,具有一个最佳的负载量.Pd、Pt的添加提高了氮氧化物的去除率,拓宽了反应活化温度的窗口,同时具有较强的抑制N₂O生成的能力.此外采用XRD、TPR等技术对Ni/H-USY体系催化剂的物相结构及氧化还原性能进行了研究,初步探讨了催化剂的催化活性与活性中心的大小与分布之间的关系.     

Pt-ZSM-5/Pd-ZSM-5催化剂对正丁烷异构化反应性能的影响

采用贵金属Pt、Pd为活性组分,HZSM-5沸石为载体,制备正丁烷异构化催化剂,在加压连续微反-色谱装置上对催化剂的反应性能进行考察。结果表明,负载Pt的贵金属催化剂在350℃具有较好的活性和选择性,在该温度下,HZSM-5沸石负载质量分数0.3%的Pt时,异丁烷选择性为40.0%,在相同温度下负载质量分数0.3%Pd时,异丁烷选择性为32.9%。     

微纤包结细粒子结构化微燃烧器的催化燃烧性能

具有三维微米孔道的烧结Ni微纤包结Pt/Al2O3细粒子催化剂复合材料结构化于毫米尺度流道中的微催化燃烧器,可以作为微型吸热反应的热量来源.考察了操作条件及Pt负载量对微燃烧器中氢气/空气催化燃烧性能的影响,并对催化剂进行了表征.结果表明处于爆炸极限内的氢气催化燃烧反应可以在微燃烧器中安全进行,过高Pt负载量会降低催化燃烧性能.在反应温度83℃,体积空速2.0×105 h-1,氢气入口摩尔分数28.5%,负载5%质量分数Pt的条件下,氢气转化率高达92-2%.     

Pt/Pt-Ce/γ-Al2O3催化氧化甲苯研究

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。     

Pt/Pt-Ce/γ-Al_2O_3催化氧化甲苯研究

通过等体积浸渍法制备单贵金属Pt/γ-Al_2O_3和双金属Pt-Ce/γ-Al_2O_3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-Al_2O_3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-Al_2O_3催化剂的催化活性最高。Pt-Ce/γ-Al_2O_3催化剂的甲苯转化率高于Pt/γ-Al_2O_3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。     

Cu负载量对CuO/γ-Al_2O_3催化低浓度甲烷燃烧性能的影响

采用浸渍法制备了CuO/γ-Al_2O_3催化剂,用于低浓度甲烷(甲烷体积分数0. 7%)催化燃烧反应,考察了Cu负载量对催化剂性能的影响,并运用SEM、XPS对催化剂进行了表征。结果表明,不同Cu负载量的催化剂中铜均处于Cu2+氧化态,同时,当催化剂Cu负载量低于7%时,随着Cu负载量的增加甲烷转化率逐渐升高,但当Cu负载量继续增加至10%时,低浓度甲烷催化燃烧反应的表观活化能升高、甲烷转化率降低。SEM和XPS表明,Cu负载量达到10%时,CuO晶体颗粒变大、Cu周围电子云密度升高、活性组分分散性变差,从而影响了催化剂的催化性能。     

助剂Ba对Pd/Al_2O_3和Pt/Al_2O_3催化剂的C1-C3烷烃催化燃烧性能的影响

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。     

Superior catalytic behaviour of Pt-doped Pd catalysts in the complete oxidation of methane at low temperature

The catalytic combustion of methane at low temperature under lean conditions was investigated over bimetallic palladium-platinum catalysts supported on alumina. Pd-Pt catalysts with constant 2 wt.% metal loading and varying compositions in Pt and Pd were prepared by successive impregnations of the metal salts. The catalysts were characterised by powder X-ray diffraction, transmission electron microscopy/electron dispersion X-ray spectroscopy (TEM/EDX), volumetry of H₂ chemisorption, FTIR study of CO adsorption and temperature-programmed oxidation (TPO). In the absence of water added to the feed, the methane conversion over Pd-rich bimetallic catalysts (Pt/Pt + Pd molar ratios less than 0.3) was found to be the same as that of the reference Pd/Al₂O₃ catalyst. Interestingly, under wet conditions, these bimetallic catalysts exhibited an improved performance with respect to Pd/Al₂O₃. This effect was found to be maintained upon mild steam ageing. An interaction between both metals was suggested to explain the enhanced activity of bimetallic catalysts. This was confirmed by TPO experiments indicating that formation and decomposition of PdO is affected upon Pt addition even for very low amounts of Pt. The adsorption of CO on reduced catalysts studied by FTIR revealed new types of adsorbed CO species, suggesting again an interaction between two metals.     

过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧性能的影响

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。     

低负载Pd/Al2O3催化剂的制备及其对CO室温催化性能研究

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...     

Non-steady activity during methane combustion over Pd/Al2O3 and the influences of Pt and CeO2 additives

Methane combustion over Pd/Al₂O₃ catalysts with and without added Pt and CeO₂ 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/Al₂O₃, which was greatly enhanced over Pd–Pt/Al₂O₃. 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/Al₂O₃ and Pd/Al₂O₃. Such non-steady behaviour was almost eliminated over Pd/Al₂O₃–CeO₂. Under a very narrow range of conditions and over a Pd/Al₂O₃ packed bed, oscillation of methane combustion was observed.     

Stability of palladium-based catalysts during catalytic combustion of methane: The influence of water

The stability of methane conversion was studied over a Pd/Al₂O₃ catalyst and bimetallic Pd–Pt/Al₂O₃ catalysts. The activity of methane combustion over Pd/Al₂O₃ gradually decreased with time, whereas the methane conversion over bimetallic Pd–Pt catalysts was significantly more stable. The differences in combustion behavior were further investigated by activity tests where additional water vapor was periodically added to the feed stream. From these tests it was concluded that water speeds up the degradation process of the Pd/Al₂O₃ catalyst, whereas the catalyst containing Pt was not affected to the same extent. DRIFTS studies in a mixture of oxygen and methane revealed that both catalysts produce surface hydroxyls during combustion, although the steady state concentration on the pure Pd catalyst is higher for a fixed temperature and water partial pressure. The structure of the bimetallic catalyst grains with a PdO domain and a Pd–Pt alloy domain may be the reason for the higher stability, as the PdO domain appears to be more affected by the water generated in the combustion reaction than the alloy. Not all fuels that produce water during combustion will have stability issues. It appears that less strong binding in the fuel molecule will compensate for the degradation.     

顺丁橡胶尾气净化催化剂的研究与应用

顺丁橡胶尾气排放中主要污染物是正己烷,选择性催化氧化法是处理正己烷的主要技术。以聚乙二醇为助剂,制备Pt/Al_2O_3催化剂,利用侧线测试其催化性能,采用CO化学吸附与透射电子显微镜对催化剂进行表征。侧线测试结果表明,催化剂活性优于进口同类催化剂,250℃时,正己烷被完全氧化;CO化学吸附结果表明,Pt/Al_2O_3催化剂中贵金属分散度为75.9%,进口催化剂只有58.7%;TEM表明,Pt/Al_2O_3催化剂上金属分布更均匀。Pt/Al_2O_3催化剂应用于顺丁橡胶尾气处理,催化活性稳定。     

Pt/Al_2O_3与Pt/MgO-Al_2O_3催化剂制备及其催化氢能载体甲基环己烷脱氢反应性能

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。