Improvement of stability of out-layer MgAl2O4 spinel for a Ni/MgAl2O4/Al2O3 catalyst in dry reforming of methane

Summary The stability of Ni/-Al₂O₃ catalyst in dry reforming of methane was found to be improved by the addition of MgO into the catalyst, probably due to the formation of out-layer MgAl₂O₄ spinels, which can effectively suppress the phase transformation to form NiAl₂O₄ spinel phases, stabilize the tiny Ni crystallites and suppress carbon deposition in dry reforming of methane.     

Co3O4/CeO2 CO氧化的原位红外光谱研究

采用沉淀氧化法制备了Co₃O₄/CeO₂催化剂。分别在干、湿条件下进行了一氧化碳氧化反应研究。运用FT-IR表征手段,在钴铈复合氧化物上进行了CO吸附及CO/O₂共吸附研究。结果表明,与纯的Co₃O₄样品相比,Co₃O₄/CeO₂具有明显的抗湿气能力。Co₃O₄/CeO₂催化剂在进行CO氧化时,表面形成了类碳酸盐物种。当环境温度低于453 K时,催化剂上类碳酸盐的生成与形成类碳酸盐物种后受热分解存在着动态平衡。当环境温度高于493 K,催化剂上生成的类碳酸盐物全部受热分解。氧化铈的加入提高了催化剂的抗湿气性能。较小粒径的Co₃O₄与CeO₂产生的强相互作用可使CeO₂向Co₃O₄提供氧,因而间接提供了CO氧化需要的氧。     

助剂SiO_2对CoMo/Al2O3-SiO_2催化剂结构的影响研究

采用原位红外光谱、拉曼光谱、紫外光谱和H2-TPR表征技术对CoMo/Al_2O_3-SiO_2催化剂进行了表征。结果表明,增加CoMo/Al_2O_3-SiO_2催化剂中的SiO_2含量会促进八面体配位钼物种向四面体配位钼物种转变,SiO_2含量越高这种结构转变趋势越显著。在CoMo/Al_2O_3催化剂载体中加入适量的SiO_2能够改变载体与活性金属的相互作用,提高了催化剂加氢脱硫活性。     

H2-induced CO adsorption and dissociation over Co/Al2O3 catalyst

The activation of adsorbed CO is an important step in CO hydrogenation. The results from TPSR of pre-adsorbed CO with H2 and syngas suggested that the presence of H2 increased the amount of CO adsorption and accelerated CO dissocia-tion. The H2 was adsorbed first, and activated to form H* over metal sites, then reacted with carbonaceous species. The oxygen species for CO2 formation in the presence of hydrogen was mostly OH*, which reacted with adsorbed CO subsequently via CO*+OH* → CO2*+H*; however, the direct CO dissociation was not excluded in CO hydrogenation. The dissociation of C-O bond in the presence of H2 proceeded by a concerted mechanism, which assisted the Boudourd reaction of adsorbed CO onthe surface via CO*+2H* → CH*+OH*. The formation of the surface species (CH) from adsorbed CO proceeded as indicated with the participation of surface hydrogen, was favored in the initial step of the Fischer-Tropsch synthesis.     

High coke-resistance of K-Ca-promoted Ni/a-Al2O3 catalyst for ch4 reforming with CO2

Summary  K-Ca-promoted Ni/&agr;-Al2O3 catalyst exhibited higher activity better coke-resistance than Ni/&agr;-Al2O3 for CH4 reforming with CO2 under different reaction conditions. Temperature-programmed activation process of CH4 reforming with CO2 was investigated on these catalysts.     

Oxidative addition of hydrogen in the “reduced” Mo/Al2O3 catalysts

An X-ray photoelectron spectroscopy study of Mo/Al₂O₃ catalysts prepared via [Mo^V ₂O₄(C₂O₄)₂(H₂O)₂]^2- complexes showed that after heating the catalysts with hydrogen in the spectrometer chamber, the position of the Mo3d line shifted to higher values of binding energy. This shift is interpreted as oxidative addition of hydrogen to the surface Mo species. A similar phenomenon was observed for a CO treated catalyst. A temperature-programmed desorption study has shown that hydrogen is strongly bounded to Mo and can only be removed from the catalysts at temperatures as high as 500°C. This revised version was published online in June 2006 with corrections to the Cover Date.     

A parametric study of methane decomposition into carbon nanotubes over 8Co-2Mo/Al2O3 catalyst

The effects of reaction temperature, partial pressure of methane, catalyst weight and gas hourly space velocity (GHSV) on methane decomposition were reported. The decomposition reaction was performed in a vertical fixed-bed reactor over 8Co-2Mo/Al 2 O 3 catalyst. The experimental results show that these four process parameters studied had vital effects on carbon yield. As revealed by the electron microscopy and Raman spectroscopy analyses, the reaction temperature and GHSV governed the average diameter, the diameter distribution and the degree of graphitization of the synthesized carbon nanotubes (CNTs). Also, an evidence is presented to show that higher temperatures and higher GHSV favored the formation of better-graphitized CNTs with larger diameters.     

光照对Pt/Al2O3光热CO2加氢反应的增强作用（英文）

在传统热催化材料的研究领域中,光照技术已经得到了广泛的应用,从而使传统热催化剂的催化反应活性和选择性得到优化.然而,在光热协同催化反应过程中,光照因素对催化反应过程的影响尚未得到很好地研究和理解.本文通过浸渍法制得Pt/Al2O3催化剂,并应用于光热协同催化CO2加氢反应.结果证明,在光热协同CO2加氢催化反应中, Pt/Al2O3催化剂表现出光热协同效应.本文结合原位漫反射红外光谱(operandoDRIFTS)和密度泛函理论计算(DFT)对光照因素对该催化反应过程的作用机制进行了进一步深入研究.结果表明, CO气体分子从Pt纳米颗粒上的脱附过程为CO2加氢反应的重要步骤;CO气体分子在Pt纳米颗粒上脱附的位置包含台阶位置(Ptstep)和平台位置(Ptterrace).结果表明,反应过程中CO气体分子从Pt表面的脱附有利于催化剂暴露出Pt反应活性位点.值得注意的是,在光热协同催化CO2加氢反应过程中,光照和温度因素对CO气体分子的脱附过程具有不同影响.吸附能的计算结果证明, CO气体分子吸附在Ptstep和Ptterrace上的吸附能分别为-1.24和-1.43eV.由此可见, CO气体分子与Pt纳米颗粒上的Ptstep吸附位点之间相互作用更强.在无光照作用的条件下对催化剂进行加热, CO气体分子更容易从Ptterrace吸附位点发生脱附;但是在对应的温度下加入光照作用后,吸附在Ptstep位点上的CO气体分子会先转移到Ptterrace吸附位点上,随后脱附,从而促进CO2加氢反应的进行.     

Improvement of stability of a Fe/Mg/Al2O3 catalyst for the decomposition of methane in the presence of O2/CO2

The stability of an Fe/Al₂O₃ catalyst in the methane decomposition in the presence of O₂/CO₂ was found to be improved by the addition of Mg into the catalyst (Mg/Fe=1/1 wt ratio), probably due to suppression of carbon deposition even under CH₄/ O₂/CO₂ (80/10/5 vol. ratio) conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

CO oxidation over Au/Al2O3catalysts modified by MgO

Summary Au/Al₂O₃catalysts modified by MgO were tested in CO oxidation using temperature programmed technique. Contrary to Au/Al₂O₃the modified Au/MgO-Al₂O₃catalysts showed high activity in the sub-ambient and ambient temperature ranges.     

Study on Au/Al2O3 catalysts for low-temperature CO oxidation in situ FT-IR

Au/Al2O3 catalyst was prepared by a modified anion impregnation method and investigated with respect to its initial activity and stability for low-temperature CO oxidation. The activity changes of the catalyst were examined after separate treatment in CO+O2 or CO2+O2. Furthermore, in situ FT-IR studies were performed to investigate the species on the surface when CO or CO+O2 or CO2+O2 was selected separately as adsorption gas. The results showed that Au/Al2O3 catalyst exhibited very high initial activity, but the catalytic activity was found to decrease gradually during CO oxidation with time on stream. And also, the activity of the catalyst declined after treatment in CO+O2 or CO2+O2. The formation and accumulation of carbonate-like species during CO oxidation or treatment in CO+O2 or CO2+O2 might be mainly responsible for the activity decrease, which was reversible.     

TiO2对Ni/Al2O3催化剂CO甲烷化性能的影响

采用溶胶凝胶法制备了一系列不同TiO₂含量的TiO₂-Al₂O₃复合载体,并通过浸渍法制备了NiO/TiO₂-Al₂O₃催化剂。分别考察了不同TiO₂含量的NiO/TiO₂-Al₂O₃催化剂及反应温度对CO甲烷化催化性能的影响。实验结果表明,当复合载体中TiO₂质量分数为30%,反应温度为350～450 ℃时,催化剂催化活性较高。利用N₂吸附-脱附(BET)、X射线衍射(XRD)及H₂程序升温还原(H₂-TPR)等手段对催化剂物化性能进行了表征。结果表明,加入适量的TiO₂能抑制镍铝尖晶石NiAl₂O₄物种的生成,改善NiO的表面分散性能,避免大晶粒NiO的形成,也改善了催化剂的还原性能,从而提高催化剂的CO甲烷化活性。     

Pt/Al2O3和Pt-Cu/Al2O3催化CCl4氢化脱氯反应

制备了Al2O3负载Pt单金属催化剂和负载Pt-Cu双金属催化剂,比较了二者不同还原温度对其催化CCl4氢化脱氯反应性能的影响。 单金属Pt催化剂上主要生成CHCl3,而双金属Pt-Cu催化剂上产物随催化剂制备时的还原温度不同而异,当催化剂经400 ℃用H2还原后产物主要为CHCl3,而当催化剂经800 ℃用H2还原后产物主要为CCl2CCl2。 由于CCl4氢化反应是强放热反应,催化剂表面局部过热使得在反应中生成的C2等产物聚合结焦,覆盖了催化剂的活性中心,导致催化剂失活。 因此,通过加入甲醇作为稀释剂以带走部分反应热可提高催化剂的稳定性。 同时也降低了CHCl3的选择性,提高了CCl2CCl2的选择性。     

La2O3助剂对Au/TiO2催化氧化CO性能的影响

采用溶胶-凝胶法制备了TiO2以及La2O3-TiO2载体, 再用沉积沉淀法制备Au/TiO2和Au/La2O3-TiO2催化剂, 并对催化剂的CO氧化反应活性进行测试. 结果表明, La2O3助剂可以显著提高催化剂催化氧化CO的活性. X射线衍射(XRD)、程序升温脱附(TPD)、N2吸附-脱附(BET)表征结果表明, La2O3助剂不仅提高了催化剂比表面积, 抑制了TiO2晶粒尺寸的长大, 并且增强了TiO2的晶格应变, 在O2气氛吸附过程中主要在TiO2表面形成O-物种. 原位傅立叶变换红外(FT-IR)结果进一步表明, La的掺杂不仅提高了吸附在Au活性位CO的氧化速率, 还使TiO2表面形成第二种活性位, 从而显著提高了催化活性.     

铝源对Ni/Al2 O3催化剂结构及其CO2-CH4重整性能的影响

以三种不同铝源采用溶液燃烧法制备了系列Ni/Al_2O_3催化剂,通过XRD、H_2-TPR、NH_3-TPD、N_2吸附-脱附、TGDTG和TPH等分析方法对反应前后催化剂进行了表征,研究了铝源对Ni/Al_2O_3催化剂结构、表面性质及其CO_2-CH_4重整性能的影响。结果表明,以Al(NO_3)_3·9H_2O为铝源制备的NiNO-AlNO催化剂比表面积较大,达102 m~2/g;高温还原峰面积大,峰型更为弥散;且载体Al_2_O_3具有一定的结晶性。而以Al_2(SO_4)_3·18H_2O和AlCl_3·6H_2O为铝源制备的NiNO-AlSO和NiNO-AlCl催化剂,其载体以无定型Al_2O_3存在,活性组分Ni晶粒粒径大、分散性差,还原峰面积较小,与载体的相互作用较弱。其中,由于硫酸铝较为稳定,需要在更高温度下才能转化为Al_2O_3,且所制备NiNO-AlSO催化剂中残留有含硫物质,使得其表面酸性较强。评价结果显示,NiNO-AlNO催化剂活性较高,稳定性好,CH4转化率为31.21%,CO_2转化率为48.97%。积炭分析结果发现,NiNO-AlNO催化剂表面积炭量最少,沉积炭主要以无定型态存在,具有良好的抗积炭性能。     

NiO/Al_2O_3催化剂上二氧化碳气氛下异丁烷耦合脱氢制异丁烯

研究了二氧化碳气氛下NiO/Al2O3催化剂上异丁烷脱氢制异丁烯的反应性能,考察了助剂K2O对NiO/Al2O3催化性能的影响。结果表明,与在惰性气氛下的反应相比,在二氧化碳气氛下异丁烷脱氢与逆水煤气变换反应耦合,促进了异丁烷脱氢反应,异丁烯的收率得到提高。助剂K2O的加入,能降低催化剂的酸性,减缓反应过程中催化活性物种NiO的过度还原,并抑制异丁烷裂解及积炭生成等副反应,从而提高了异丁烯的收率以及催化剂的稳定性。     

NO reduction with C3H8 on Co/Al2O3 catalyst. effect of O2 concentration

The selective catalytic reduction (SCR) of NO by propane in excess oxygen-containing gas mixture was studied on Co/Al₂O₃ catalyst. The oxygen concentration is very important for the reaction. The NO conversion to N₂ without oxygen is 3% at 800 K and when the O₂ concentration is raised up to 8% the NO conversion reaches its maximum value of 60% at 800 K. Characterization results by TPR and UV-Vis spectroscopy show that in the catalyst, species strongly interacting with tetrahedral and octahedral Co²⁺ ions in the support are present. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photocatalytic conversion of NOx on AgCl/Al2O3 catalyst

The rate of NO conversion under UV illumination was evaluated over Ag/Al₂O₃ and AgCl/Al₂O₃ catalysts at room temperature. The AgCl/Al₂O₃ catalyst is highly active for the conversion of NO_x. The conversion is enhanced in the presence of O₂ and further enhanced when oxygen coexists with hydrocarbons. Diffuse reflectance spectra of AgCl/Al₂O₃ and Ag/Al₂O₃ show an absorption band at 250 nm, and a weak and broad band at 230 nm, respectively. The high photocatalytic NO_x conversion is achieved over the AgCl/Al₂O₃ catalyst. The conversion level of NO_x is maintained above 60% over 5 h in the presence of O₂ and hydrocarbons under UV-irradiation. The absorption band at 250 nm is ascribed to the band gap energy of crystallized AgCl particles on Al₂O₃. These results suggest that high photocatalytic NO_x conversion proceeds on crystallized AgCl particles formed on Al₂O₃.     

CF4在Al2O3基金属氧化物上的分解反应

考察了在无水条件下γ-Al2O3基金属氧化物M-Al2O3(M=Mg、La、Ba、Ce、Ni、P)与CF4反应转化为金属氟化物的反应. 结果表明, 在所筛选的金属氧化物中, γ-Al2O3的初活性较高, 但由于CF4分解时产生的强放热效应使未反应的γ-Al2O3发生了α相变, 致使CF4转化率急剧下降, 反应温度越高, γ-Al2O3的α相变越快, 活性下降就越快. CF4在MgO-Al2O3上分解时, Mg物种比Al优先氟化生成了MgF2, Mg物种的氟化反应及其产生的强放热效应使MgAl2O4结构发生了解体. 在Al2O3表面负载助剂P、Ni,提高了其热稳定性, 抑制了CF4高温分解时未反应的Al2O3发生α相变, 使更多的γ-Al2O3参与了CF4分解反应.