MoO3和Nb2O5助剂对Pt/ZrO2催化剂上短链烷烃燃烧反应的不同促进作用

贵金属Pt催化剂具有高活性和热稳定性,广泛应用于催化挥发性有机物的完全氧化反应(燃烧反应).短链烷烃(甲烷、乙烷、丙烷等)化学性质稳定,是最难氧化的一类有机物,常用作考察燃烧反应催化剂性能的模型反应物.然而,目前报道的研究工作通常仅限于针对某一种烷烃底物的催化燃烧,系统考察催化剂以及助剂对不同短链烷烃的催化燃烧活性鲜有报道.在短链烷烃中,甲烷只有C–H键;而其它烷烃除了C–H键;还有C–C键.因此,研究催化剂对甲烷、乙烷和丙烷燃烧反应催化性能的差异性,对于认识催化剂上C–H键和C–C键的活化具有非常重要的意义.本文制备了MoO3或Nb2O5修饰的Pt/ZrO2催化剂并用于短链烷烃的燃烧反应.研究发现,MoO3助剂对甲烷燃烧有明显的抑制作用,但对乙烷,丙烷和正己烷燃烧反应具有促进作用,促进作用随着烷烃碳链的增长逐渐增加;Nb2O5助剂对甲烷、乙烷、丙烷和正己烷燃烧反应均具有促进作用,然而促进作用随着碳链的增长而逐渐减弱.MoO3和Nb2O5助剂的不同促进作用与助剂影响催化剂表面酸性以及Pt物种的氧化或还原态有关.NH3-TPD结果表明,MoO3助剂可以显著增加Pt/ZrO2催化剂表面强酸位点数量,而Nb2O5助剂可以显著增加Pt/ZrO2催化剂表面中强酸位点数量.HTEM结果表明,两种助剂的添加都不会明显改变Pt物种的颗粒尺寸.在Pt-Mo/ZrO2催化剂上,MoO3覆盖部分Pt物种形成丰富的Pt-MoO3界面,促进了金属Pt物种和强表面酸性位点的生成,提高了丙烷燃烧反应活性;Pt-Nb/ZrO2催化剂上载体表面的部分Nb2O5被Pt物种包覆,使得生成的表面Pt-Nb2O5界面低于Pt-Mo/ZrO2催化剂,但由于催化剂表面酸性位的提升,也促进了丙烷燃烧反应活性的提高.XPS结果表明,在甲烷燃烧反应中,Pt-Nb/ZrO2催化剂上Ptn+物种能够更加稳定地存在,这可能是Nb2O5助剂提高Pt-Nb/ZrO2催化剂上甲烷燃烧活性的关键.而Pt-Mo/ZrO2催化剂上Ptn+物种在甲烷反应中可以更容易地被还原,并且由于MoO3的包裹导致暴露的Pt位点数量降低,使催化剂催化甲烷燃烧的活性受到抑制.可见,MoO3助剂更有利于C–C键活化,而Nb2O5助剂更有利于高键能的C–H键活化.综上,本文系统性地研究MoO3助剂和Nb2O5助剂对Pt/ZrO2催化剂上不同短链烷烃的燃烧反应的影响,证实了两种助剂的促进作用与碳链长度的关系是截然不同的.     

The photocatalytic and thermal catalytic reduction of CO2 with H2 over Pt/TiO2 catalysts

浸渍法制备了Pt负载量为0.5 to 2%的Pt/TiO2催化剂,考察它们在光照和加热条件下二氧化碳催化加氢性能.结果表明,二氧化碳加氢反应均可在Pt/TiO2的催化下进行,但在不同反应条件下加氢反应通过不同方式进行.在加热条件下,二氧化碳可转化为一氧化碳和甲烷,且在低温加热条件下一氧化碳是主产物(CO选择性为100%,250℃,0.5%Pt/TiO2).在1.5%Pt/TiO2催化剂上,当反应温度从250℃升高到450℃时,CH4的选择性由0增加到60.94%.同时,增加Pt的负载量也会导致CH4的选择性的增加.然而,在光照条件下,产物只有甲烷.CO2-TPD结果表明,二氧化碳通过羰基基团与作为吸附中心的Pt相连接.结合催化活性与表征结果,提出在光照条件下,反应可能以二氧化碳和氢气分别被光生电子活化反应生成甲酸中间体,随后经由甲酸加氢和脱水生成甲烷的机理进行.而在加热条件下,反应可能以二氧化碳首先吸附在催化剂表面形成羰基Pt物种,随后加氢生成一氧化碳,一氧化碳继续加氢生成甲烷的机理进行.     

光照和加热条件下Pt/TiO_2催化二氧化碳加氢(英文)

浸渍法制备了Pt负载量为0.5 to 2%的Pt/TiO2催化剂,考察它们在光照和加热条件下二氧化碳催化加氢性能.结果表明,二氧化碳加氢反应均可在Pt/TiO2的催化下进行,但在不同反应条件下加氢反应通过不同方式进行.在加热条件下,二氧化碳可转化为一氧化碳和甲烷,且在低温加热条件下一氧化碳是主产物(CO选择性为100%,250℃,0.5%Pt/TiO2).在1.5%Pt/TiO2催化剂上,当反应温度从250℃升高到450℃时,CH4的选择性由0增加到60.94%.同时,增加Pt的负载量也会导致CH4的选择性的增加.然而,在光照条件下,产物只有甲烷.CO2-TPD结果表明,二氧化碳通过羰基基团与作为吸附中心的Pt相连接.结合催化活性与表征结果,提出在光照条件下,反应可能以二氧化碳和氢气分别被光生电子活化反应生成甲酸中间体,随后经由甲酸加氢和脱水生成甲烷的机理进行.而在加热条件下,反应可能以二氧化碳首先吸附在催化剂表面形成羰基Pt物种,随后加氢生成一氧化碳,一氧化碳继续加氢生成甲烷的机理进行.     

质子交换膜燃料电池催化剂稳定化方法研究进展

Pt/C催化剂稳定性是制约质子交换膜燃料电池商业化的关键技术挑战之一,因此增强燃料电池催化剂稳定性研究一直是该领域的热点。指出Pt纳米粒子的溶解再沉积、团聚长大,中间物种在Pt表面的吸附钝化,有害杂质中毒及碳载体腐蚀是Pt/C催化剂稳定性衰减的主要因素,概述了近些年提高质子交换膜燃料电池催化剂稳定性的研究进展。指出Pt合金化、采用更稳定载体及进一步加强金属载体间相互作用是增强催化剂稳定性的发展方向。     

原子层沉积制备掺氮碳膜修饰的 Pt/CNTs 实现甲醇高效电催化氧化

甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注. 贵金属 Pt 是甲醇燃料电池阳极催化剂不可缺少的活性组分, 但 Pt 价格昂贵, 易与 CO 等中间体强相互作用而中毒失活, 从而限制了甲醇燃料电池的广泛应用. 因此, 如何提高Pt 的利用率成为一个关键问题. 研究表明, 在碳材料载体中掺杂氮元素, 改变了载体本身的表面结构和电子性质, 有利于Pt 颗粒的成核和生长, 可获得尺寸小、分布均匀的 Pt 纳米颗粒, 能显著提升催化反应活性和 Pt 利用率. 然而, 传统的氮掺杂方法需要在高温、高压及氨气条件下进行, 增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术, 能够在原子级别精确控制膜的厚度, 既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰. 本课题组利用原子层沉积技术优势, 首先在碳纳米管表面沉积了直径 2 nm 左右的 Pt纳米颗粒, 然后在 Pt 纳米颗粒外表面超薄修饰聚酰亚胺膜, 通过后处理得到多孔掺氮碳膜修饰的 Pt/CNTs 催化剂. 碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制. 结果表明, 适当厚度的碳膜修饰 Pt/CNTs 催化剂可显著提升其甲醇电氧化性能, 电流密度可达商业 20% Pt/C 的 2.7 倍, 催化剂稳定性也显著改善. 然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现, 超薄修饰碳膜后催化剂活性表面积有所降低, 这是由于碳膜的覆盖导致表面 Pt原子数减少. 修饰前后催化剂颗粒尺度变化不大, 推测催化剂活性的提高与形成了有利于催化反应的 Pt-碳膜界面有关.然而, 当碳膜修饰层过厚时, 会导致反应物分子难以扩散到 Pt 颗粒表面, 使催化剂活性降低. 预吸附单层 CO 溶出实验结果表明, 多孔掺氮碳膜超薄修饰 Pt/CNTs 催化剂后, CO 氧化峰的起始电位和峰值电位都向低电位处偏移, 这表明 Pt 表面吸附的 CO 在较低电位下即可被氧化, CO 更容易从 Pt 表面移除, 从而提高了催化剂的抗 CO 毒化能力. X 射线光电子能谱实验结果进一步表明, 经多孔掺氮碳膜修饰后, Pt 的 4f 电子向高结合能处偏移, 表明 Pt 原子周围的电子密度减小, 从而弱化了 Pt 对 CO 吸附的σ-π键反馈作用, 即减弱了 Pt 原子对 CO 的吸附, 这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因.     

原子层沉积制备掺氮碳膜修饰的Pt/CNTs实现甲醇高效电催化氧化（英文）

甲醇燃料电池作为一种清洁、高效的能源转化形式广受关注.贵金属Pt是甲醇燃料电池阳极催化剂不可缺少的活性组分,但Pt价格昂贵,易与CO等中间体强相互作用而中毒失活,从而限制了甲醇燃料电池的广泛应用.因此,如何提高Pt的利用率成为一个关键问题.研究表明,在碳材料载体中掺杂氮元素,改变了载体本身的表面结构和电子性质,有利于Pt颗粒的成核和生长,可获得尺寸小、分布均匀的Pt纳米颗粒,能显著提升催化反应活性和Pt利用率.然而,传统的氮掺杂方法需要在高温、高压及氨气条件下进行,增加了催化剂制备难度和成本.原子层沉积技术是逐层超薄沉积技术,能够在原子级别精确控制膜的厚度,既可制备尺度均一、高度可控的纳米粒子,也能实现材料表面的可控超薄修饰.本课题组利用原子层沉积技术优势,首先在碳纳米管表面沉积了直径2 nm左右的Pt纳米颗粒,然后在Pt纳米颗粒外表面超薄修饰聚酰亚胺膜,通过后处理得到多孔掺氮碳膜修饰的Pt/CNTs催化剂.碳膜的厚度可简单通过调控聚酰亚胺膜的沉积厚度来控制.结果表明,适当厚度的碳膜修饰Pt/CNTs催化剂可显著提升其甲醇电氧化性能,电流密度可达商业20%Pt/C的2.7倍,催化剂稳定性也显著改善.然而碳膜修饰过厚会导致催化剂活性降低.通过计算催化剂电化学活性表面积发现,超薄修饰碳膜后催化剂活性表面积有所降低,这是由于碳膜的覆盖导致表面Pt原子数减少.修饰前后催化剂颗粒尺度变化不大,推测催化剂活性的提高与形成了有利于催化反应的Pt-碳膜界面有关.然而,当碳膜修饰层过厚时,会导致反应物分子难以扩散到Pt颗粒表面,使催化剂活性降低.预吸附单层CO溶出实验结果表明,多孔掺氮碳膜超薄修饰Pt/CNTs催化剂后,CO氧化峰的起始电位和峰值电位都向低电位处偏移,这表明Pt表面吸附的CO在较低电位下即可被氧化,CO更容易从Pt表面移除,从而提高了催化剂的抗CO毒化能力.X射线光电子能谱实验结果进一步表明,经多孔掺氮碳膜修饰后,Pt的4f电子向高结合能处偏移,表明Pt原子周围的电子密度减小,从而弱化了Pt对CO吸附的σ-π键反馈作用,即减弱了Pt原子对CO的吸附,这是导致掺氮碳膜修饰后催化剂活性及稳定性都大幅提高的原因.     

氮杂石墨烯碳纳米管复合材料负载Pt催化剂在甘油选择性氧化中的应用（英文）

生物柴油因原材料来源广、可再生、安全性能好、环境友好及可替代石化柴油等优势被认为是一种极有发展前景的可再生能源,正逐步成为当今国际新能源开发的热点.作为生物柴油生产过程的主要副产物,甘油多相氧化制备具有高附加值的氧化产物是生物柴油产业链上的重要分支.目前,应用于该催化氧化体系的催化剂主要为负载型单金属(Au,Pd和Pt)和双金属(Au-Pd,Au-Pt和Pt-Bi)催化剂.其中,Au催化剂在碱性条件下对甘油氧化反应有较高的催化活性和甘油酸选择性,并且该催化剂稳定性高,不易在较高氧气压力的反应条件下因氧中毒而失活.但是,由于反应过程中碱的存在,反应体系中部分产物间可相互转化,从而掩盖催化剂的产物选择性本质,增大了产物分析、分离和催化剂作用机理研究的难度.而Pd和Pt催化剂不受酸、碱反应条件的限制,能够在无碱助剂作用下实现甘油催化氧化.与Au基和Pd基催化剂相比,Pt基催化剂可实现在酸性或中性反应条件下甘油选择性氧化产物的一步生成,同时具有较高的催化活性及稳定性,且氧化产物收率较高.一直以来,以碳材料为载体负载的金属催化剂被广泛应用于甘油液相氧化反应.研究表明,催化剂活性与碳的孔径分布有关,随着碳载体微孔比例的增加,催化剂活性下降.此外,载体表面基团对金属活性有着重要影响.例如,载体表面含氧基团的吸电子作用可降低载体表面电子的流动性(电子密度和导电性),从而阻碍甘油氧化反应过程中OH–的吸附和再生,导致反应活性降低.因此,开发微孔比例小、富含负电性基团的碳载体成为甘油氧化过程中急需解决的问题之一.本文通过热解碳纳米管(MWCNTs)和三聚氰胺的混合物,在碳纳米管表面直接生长得到氮杂石墨烯(NG-MWCNTs),并采用SEM,N_2吸附,TEM和XRD对所得复合材料进行了表征.实验发现,相比于单纯的MWCNTs和直接热解三聚氰胺所得的产物CN_x,NG-MWCNTs具有更高的比表面积(173 m~2/g)和更大的平均孔径.此外,NG-MWCNTs非常适合作为Pt催化剂的载体,Pt平均粒径可小至1.4±0.4 nm.所制备的Pt/NG-MWCNTs催化剂在甘油选择性氧化反应中具有很高的催化活性和甘油酸选择性(甘油转化率和甘油酸选择性分别可达64.4%和81.0%),且具有可重复使用性能.Pt/NG-MWCNTs催化剂优异的催化活性不仅与载体表面高分散的Pt有关,而且与N原子对Pt的给电子作用有关.     

Co/Zr/Al2O3-Pt/ZSM-5催化剂的制备及其合成气转化制液体燃料性能研究

以Co基催化剂耦合沸石分子筛催化剂应用于合成气催化转化可以有效改善催化剂的产物选择性。本研究通过浸渍法制备得到Zr/Al₂O₃载体和Pt/ZSM-5催化剂,再通过超声分散法制备了Co/Al₂O₃、Co/Zr/Al₂O₃和Co/Zr/Al₂O₃-Pt/ZSM-5催化剂。通过系列表征技术对载体和催化剂理化性质进行分析,评价了催化剂费-托合成反应性能。结果表明,Zr的引入有助于提升Co/Zr/Al₂O₃上Co物种的还原性,改善催化活性,增加C12+重质烃的选择性。当Co/Zr/Al₂O₃与Pt/ZSM-5耦合后,由于贵金属Pt的助剂效应,进一步促进Co物种的还原,Co/Zr/Al₂O₃-Pt/ZSM-5催化剂的CTY值提高至8.3×10^-5 mmol/(g·s),同时...     

氮杂石墨烯碳纳米管复合材料负载Pt催化剂在甘油选择性氧化中的应用

一直以来,以碳材料为载体负载的金属催化剂被广泛应用于甘油液相氧化反应.研究表明,催化剂活性与碳的孔径分布有关,随着碳载体微孔比例的增加,催化剂活性下降.此外,载体表面基团对金属活性有着重要影响.例如,载体表面含氧基团的吸电子作用可降低载体表面电子的流动性(电子密度和导电性),从而阻碍甘油氧化反应过程中OH–的吸附和再生,导致反应活性降低.因此,开发微孔比例小、富含负电性基团的碳载体成为甘油氧化过程中急需解决的问题之一.本文通过热解碳纳米管(MWCNTs)和三聚氰胺的混合物,在碳纳米管表面直接生长得到氮杂石墨烯(NG-MWCNTs),并采用SEM,N2吸附,TEM和XRD对所得复合材料进行了表征.实验发现,相比于单纯的MWCNTs和直接热解三聚氰胺所得的产物CNx,NG-MWCNTs具有更高的比表面积(173 m2/g)和更大的平均孔径.此外,NG-MWCNTs非常适合作为Pt催化剂的载体,Pt平均粒径可小至1.4±0.4 nm.所制备的Pt/NG-MWCNTs催化剂在甘油选择性氧化反应中具有很高的催化活性和甘油酸选择性(甘油转化率和甘油酸选择性分别可达64.4%和81.0%),且具有可重复使用性能.Pt/NG-MWCNTs催化剂优异的催化活性不仅与载体表面高分散的Pt有关,而且与N原子对Pt的给电子作用有关.     

Ni/Al2 O3 催化剂上甲烷的分解温度和时间对积炭的影响

用在线质谱法研究了Ni/Al2O3催化剂上甲烷分解温度和时间对积炭的影响。实验结果表明：在600～800℃内甲烷在还原的Ni/Al2O3催化剂上可分解为表面碳物种（即NiXC）和氢气,这种表面碳物种在较低的温度下可扩散进入体相,在高温下可逐步转化为低活性的碳物种。在800℃下由于表面碳物种不能扩散进入体相,金属镍中心迅速被表面碳物种覆盖,导致甲烷分解反应失活。     

Fe-Zn-Zr/分子筛复合催化剂上CO2加氢合成异构烷烃Ⅰ.不同分子筛对催化剂性能的影响

 在Fe-Zn-Zr/分子筛复合催化剂上考察了不同类型的分子筛对CO2加氢反应性能的影响. 结果表明,不同分子筛对复合催化剂性能的影响不同,Fe-Zn-Zr/HY是合成异构烷烃有效的复合催化剂. 分子筛的酸性及酸强度对复合催化剂性能有较大的影响,中等强度和较高强度的酸性位有利于异构烃的生成.     

Pretreatment of Alumina and Its Influence on the Properties of Co/Alumina Catalysts for Fischer-Tropsch Synthesis

16.6%Co/γ-Al_2O_3 catalysts prepared by incipient wetness impregnation method were used for Fischer-Tropsch synthesis.The support was pre-treated with different concentration of NH_4NO_3 aqueous solution.The effect of support pre-treatment on the properties of support and performance of supported- cobalt-based catalysts was investigated.To treat the support with NH_4NO_3 aqueous solution enlarged the pore ofγ-Al_2O_3,decreased the impurity Na_2O content,and weakened the surface acidity ofγ-Al_2O_3. The change in the properties of the support decreased the interaction between cobalt species and support, enhanced the CO hydrogenation rate and the C_(5 )selectivity.For all catalysts,increasing the reaction temperature increased the CO hydrogenation rate or the CO conversion,slightly decreased the total hydrocarbon selectivity,and favored the formation of methane and light hydrocarbons,while the chain growth probability decreased.For 16.6%Co/γ-Al_2O3 catalysts,prepared with the support treated with 100 g/L NH_4NO3 aqueous solution,the CO conversion,the CH_4 selectivity,and the C_(5 )selectivity were 83.13%,6.86% and 82.75% respectively,and the chain growth probability was 0.83 under the condition of 493 K,1.5 MPa,500 h~(-1)and the molar ratio of H_2 to CO being 2.0 in feed.     

Ethylene Conversion to Higher Hydrocarbon over Copper Loaded BZSM-5 in the Presence of Oxygen

The successful production of higher hydrocarbons from methane depends on the stability or the oxidation rate of the intermediate products. The performances of the BZSM-5 and the modified BZSM-5 catalysts were tested for ethylene conversion into higher hydrocarbons. The catalytic experiments were carried out in a fixed-bed micro reactor at atmospheric pressure. The catalysts were characterized using XRD, NH3-TPD, and IR for their structure and acidity. The result suggests that BZSM-5 is a weak acid. The introduction of copper into BZSM-5 improved the acidity of BZSM-5. The conversion of ethylene toward higher hydrocarbons is dependent on the acidity of the catalyst. Only weaker acid site is required to convert ethylene to higher hydrocarbons. The loading of Cu on BZSM-5 improved the selectivity for higher hydrocarbons especially at low percentage. The reactivity of ethylene is dependent on the amount of acidity as well as the presence of metal on the catalyst surface. Cu1%BZSM-5 is capable of converting ethylene to higher hydrocarbons. The balances between the metal and acid sites influence the performance of ethylene conversion and higher hydrocarbon selectivity. Higher loading of Cu leads to the formation of COx.     

Cyclohexene Reactivity Using Catalysts Containing Pt,Re and PtRe Supported on Na‐ and H‐Mordenite

The reactivity of cyclohexene (CHE) over catalysts containing 0.3 wt% Pt, 0.3 wt% Re or 0.3 wt% Pt + 0.3 wt% Re supported on Na‐ and H‐mordenite has been studied in an atmospheric flow‐type reactor at a temperature range of 100–400 °C, using a flow of hydrogen (20 cm³/min). The catalysts were characterized for acid sites strength‐distribution, using desorption of ammonia in DSC. The acidity of H‐mordenite (HM) is attributed to strong acid sites, whereas the acidity of Na‐mordenite (NaM) is due to weak acid sites which are not involved in the catalytic reaction under study. The catalysts containing HM enhance the reactivity of CHE for isomorization reactions. However, the reactivity of CHE on NaM catalysts enhances only the hydrogenation and dehydrogenation reactions. Pt/HM is the most selective catalyst for isomerization of CHE, whereas Pt/NaM and PtRe/NaM catalysts are the most selective for hydrogenation and dehydrogenation reactions, respectively. The hydroisomorization of CHE seems to depend only on the acidity of the catalysts, whereas both hydrogenation and dehydrogenation reactions were controlled by metallic function of the catalysts.     

Direct conversion of natural gas to higher hydrocarbons: A review

Direct conversion of methane to higher hydrocarbons is an effective process to solve the problem of natural gas utilization. Although remarkable progress has been achieved on the dehydro-aromatization of methane (DAM), low conversion caused by severe thermodynamic limitations, coke formation, and catalysis deactivation remain important drawbacks to the direct conversion process. Molybdenum catalysts supported on HZSM-5 type zeolite support are among the most promising catalysts. This review focuses on the aspects of direct methane conversion, in terms of catalysts containing metal and support, reaction conditions, and conversion in different types of reactors. The reaction mechanism for this catalytic process is also discussed.     

Aromatization of methane by using propane as co-reactant over cobalt and zinc-impregnated HZSM-5 catalysts

The activities of the cobalt and zinc-impregnated HZSM-5 catalysts to the non-oxidative conversion of propane (C3) and methane (C1) into aromatic hydrocarbons were evaluated using a fixed-bed microreactor. C1 conversion reached 36.7% and the selectivity of aromatic products reached above 88.7% at atmospheric pressure, weight (hourly) space velocity (WHSV) 1.6 g h⁻¹/(g cat)⁻¹ and 873 K. The influence of the acidity and the ratio of cobalt in the catalyst on the conversion of methane and propane was evaluated. C1 incorporation was conclusively confirmed by the mass spectral analyses of aromatic products produced in a run with ¹³CH₄ which shows a significant ¹³C enrichment in the C₆H₆⁺, C₇H₈⁺ and C₈H₁₀⁺ fragments. The methane activation could result from its hydrogen-transfer reaction with alkenes. These catalysts were thoroughly characterized using XRD, N₂ adsorption measurements, TPD of NH₃, and FT-IR. The results showed that the activation of methane in low temperature was due to existence of propane. The acidic changes and micropore area of the catalyst severely affected aromatization, and resulted in drastic modifications in product distribution. From this work, we found that only a small fraction of tetrahedral framework aluminum, which corresponds to the Bronsted acid sites, is sufficient to accomplish the aromatization of the intermediates in methane and propane aromatic reaction, while the superfluous strong Bronsted acid sites, which can be decreased by adding Co and Zn, are showed to be related with the aromatic carbonaceous deposits on the catalysts. The density of acidic site and the strength of strong acid decreased when the concentration of Co and Zn in the catalyst increased. Therefore, a much higher benzene yield and a longer durability of the catalysts are obtained when compared with the conventional HZSM-5 catalysts.     

n-hydrocarbons conversions over metal-modified solid acid catalysts

The quality of a straight-run fuel oil can be improved if saturated n-hydrocarbons of low octane number are converted to their branched counterparts. Poor reactivity of traditional catalysts in isomerization reactions imposed the need for the development of new catalysts among which noble metal promoted acid catalysts, liquid and/or solid acid catalysts take a prominent place. Sulfated zirconia and metal promoted sulfated zirconia exhibit high activity for the isomerization of light alkanes at low temperatures. The present paper highlights the original results which indicate that the modification of sulfated zirconia by incorporation of metals (platinum and rhenium) significantly affects catalytic performances in n-hydrocarbon conversion reactions. Favourable activity/selectivity of the promoted sulfated zirconia depends on the crystal phase composition, critical crystallites sizes, platinum dispersion, total acidity and type of acidity. Attention is also paid to the recently developed solid acid catalysts used in other conversion reactions of hydrocarbons.     

一氧化碳加氢制碳氢化合物反应选择性的调控

合成气（即一氧化碳加氢）催化转化制碳氢化合物的费托合成反应是煤、甲烷和生物质等非油基碳资源间接转化制液体燃料或化学品的关键步骤．在传统的费托合成催化荆上,产物服从Anderson．Schulz．Flory分布,特定产物的选择性差．设计和制备高选择性费托合成催化剂,实现C-C偶联产物选择性的调控,是现代C,化学最具挑战性的课题．本文概述了近年来有关c￡偶联机理方面的理论研究进展,简要总结了影响费托合成产物选择性的几个关键因素,着重阐述了活性金属尺寸及所处微环境对产物选择性和催化：舌性的影响．本文还评述了既具有一氧化碳加氢制高碳烃又具有高碳烃加氢裂解能力的双功能费托合成催化剂体系,并提出通过控制加氢裂解等二次反应控制费托合成产物选择性的新策略．     

Dual-Bed Catalytic System for Direct Conversion of Methane to Liquid Hydrocarbons

A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650-800℃), methane to oxygen ratio (4 10), and SiO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH:j techniques. The rise in oxygen concentration is not beneficial for the C5 selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO CO2) products is more dominant than the oligomerization reaction. The dual-bed catalytie system is highly potential for directly converting methane to liquid fuels.     

助剂钾对二氧化碳加氢反应活性及产物分布的影响

报导助剂Ｋ对Ａｌ２Ｏ３，ＴｉＯ２，ＺｒＯ２担载Ｆｅ催化剂，用于ＣＯ２加氢合成Ｃ２＋烃的催化活性及产物分布的影响。与不含Ｋ的催化剂相比，Ｋ的存在导致Ｆｅ／Ｋ－Ａｌ２Ｏ３的催化活性及Ｃ＾２＋烃选择性明显提高，但使Ｆｅ／Ｋ－ＴｉＯ２的催化活性及Ｃ２＋烃选择性显著下降，而对Ｆｅ／Ｋ－ＺｒＯ２，这种影响并不显著。Ｋ的明显有利于低碳烯烃的生存。