Influence of MgO contents on silica supported nano-size gold catalyst for carbon monoxide total oxidation

A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, O2 temperature-programmed desorption （O2-TPD）, and inductively coupled with plasma atomic emission spectroscopy （ICP-AES） techniques. The total oxidation of CO was chosen as the probe reaction. The results suggest that for the gold catalysts supported on the silica material after MgO modification, the size of the gold particles is pronouncedly reduced, the oxygen mobility is enhanced, and the catalytic activity for low-temperature CO oxidation is greatly improved. The gold catalyst modified by 6 wt% MgO （Mg/SiO2 weight ratio） shows higher CO oxidation activity, over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.

Gold/Mg-Al mixed oxides catalysts for oxidative esterification of methacrolein:Effects of support size and composition on gold loading

Gold catalysts supported on Mg-Al mixed oxides for oxidative esterification of methacrolein are prepared by impregnation.Effects of the support particle size,concentration of HAuCl4 solution and Mg/Al ratio on gold loading and catalytic properties are investigated.The catalysts are characterized by CO_(2)-TPD,EDS,XPS,STEM and XRD techniques.Catalysts with smaller support particle size show more uniform gold distribution and higher gold dispersion,resulting in a higher catalytic performance,and the uniformity of gold and the activity of the catalysts with larger support particle size can be improved by decreasing the concentration of HAuCl4 solution.The Mg/Al molar ratio has significant effect on the uniformity of gold and the activity of the catalyst,and the optimum Mg/Al molar ratio is 0.1–0.2.This study underlines the importance of engineering support particle size,concentration of HAuCl4 solution and density of adsorption sites for efficient gold loading on support by impregnation.

Micro-aluminum powder with bi-or tri-component alloy coating as a promising catalyst:Boosting pyrolysis and combustion of ammonium perchlorate

A novel design of micro-aluminum(μAl)powder coated with bi-/tri-component alloy layer,such as:Ni-P and Ni-P-Cu(namely,Al@Ni-P,Al@Ni-P-Cu,respectively),as combustion catalysts,were introduced to release its huge energy inside Al-core and promote rapid pyrolysis of ammonium perchlorate(AP)at a lower temperature in aluminized propellants.The microstructure of Al@Ni-P-Cu demonstrates that a three-layer Ni-P-Cu shell,with the thickness of~100 nm,is uniformly supported byμAl carrier(fuel unit),which has an amorphous surface with a thickness of~2.3 nm(catalytic unit).The peak temperature of AP with the addition of Al@Ni-P-Cu(3.5%)could significantly drop to 316.2℃ at high-temperature thermal decomposition,reduced by 124.3℃,in comparison to that of pure AP with 440.5℃.It illustrated that the introduction of Al@Ni-P-Cu could weaken or even eliminate the obstacle of AP pyrolysis due to its reduction of activation energy with 118.28 kJ/mol.The laser ignition results showed that the ignition delay time of Al@Ni-P-Cu/AP mixture with 78 ms in air is shorter than that of Al@Ni-P/AP(118 ms),decreased by 33.90%.Those astonishing breakthroughs were attributed to the synergistic effects of adequate active sites on amorphous surface and oxidation exothermic reactions(7597.7 J/g)of Al@Ni-P-Cu,resulting in accelerated mass and/or heat transfer rate to catalyze AP pyrolysis and combustion.Moreover,it is believed to provide an alternative Al-based combustion catalyst for propellant designer,to promote the development the propellants toward a higher energy.

Insights into support effects on Ce-Zr-O mixed oxide-supported gold catalysts in CO oxidation

Au]Cel_xZrxO2 catalysts （x = 0-0.8） were prepared by a deposition-precipitation method using Cel_xZrxO2 nanoparticles as supports with variable Ce and Zr contents. Their structures were characterized by complimentary means such as X-ray diffraction, Raman, scanning trans- mission electron microscopy and X-ray photoelectron spectroscopy （XPS）. These Au catalysts possessed similar sizes and crystalline phases of Cel_xZrzO2 supports as well as similar sizes and oxidation states of Au nanoparticles. The oxidation state of Au nanoparticles was dominated by Au~ especially in CO oxidation. Their activities were examined in CO oxidation at different temperatures in the range of 303-333 K. The CO oxidation rates normalized per Au atoms increased with the increasing Ce contents, and reached the maximum value over Au/CeO2. Such change was in parallel with the change in the oxygen storage capacity values, i.e. the amounts of active oxygen species on Au/Cel_zZrzO2 catalysts. The excellent correlation between the two properties of the catalysts suggests that the intrinsic support effects on the CO oxidation rates is related to the effects on the adsorption and activation of O2 on Au/Cel_xZrxO2 catalysts. Such understanding on the support effects may be useful for designing more active Au catalysts, for example, by tuning the redox properties of oxide supports.

Direct gas-phase epoxidation of propylene to propylene oxide using air as oxidant on supported gold catalyst

Gold catalysts supported on SiO2, TiO2, TiO2-SiO2, and ZrO2-SiO2 supports were prepared by impregnating each support with a basic solution of tetrachloroauric acid. X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and X-ray photoelectron spectroscopy （XPS） techniques were used to characterize their structure and surface composition. The results indicated that the size of gold particles could be controlled to below 10 nm by this method of preparation. Washing gold catalysts with water could markedly enhance the dispersion of metallic gold particles on the surface, but it could not completely remove the chloride ions left on the surface. The catalytic performance of direct vapor-phase epoxidation of propylene using air as an oxidant over these catalysts was evaluated at atmospheric pressure. The selectivity to propylene oxide （PO） was found to vary with reaction time on the stream. At the reaction conditions of atmosphere pressure, temperature 325 ℃, feed gas ratio V（C3H6）/V（O2）= 1/2, and GHSV =6000h^-1, 17.9% PO selectivity with 0.9% propylene conversion were obtained at initial 10 min for Au/SiO2 catalyst. After reacting 60 min only 8.9% PO selectivity were detected, but the propylene conversion rises to 1.4% and the main product is transferred to acrolein （72% selectivity）. Washing Au/TiO2-SiO2 and Aa/ZrO2-SiO2 samples with magnesium citrate solution could markedly enhance the activity and PO selectivity because smaller gold particles were obtained.

Evolution of Gold Species in an Au/CeO_2 Catalyst and Its Impact on Activity for CO Oxidation

An Au/ceria（0.44%, mass fraction） catalyst containing gold ions was prepared by a modified deposition precipitation method, and the evolution of gold ions in the catalyst and its influence on the catalysis of CO oxidation were investigated. It was found that the as-prepared catalyst containing gold ions with high valence could fully oxidize CO at -10 ℃ initially but was deactivated gradually at low temperatures during the reaction with CO or treatment by unpurified air. The deactivation of the catalyst during CO oxidation or treatment of it by unpurified air was independent and progressive at low temperatures while the activity of the catalyst at relatively high temperatures was maintained well. During the reaction with CO or treatment by unpurified air, the XPS results indicate that gold species evolved from high valence to low valence and the diffuse reflectance UV-Vis spectra show that high valence gold was reduced to charged gold clusters, gold clusters grew to small gold crystals and small gold crystals grew to large gold particles. Accordingly, the high valence gold corresponded to the activity at low temperatures and the metallic gold was active and relatively stable at high temperatures. The turnover frequencies（TOF） of the catalysts treated by different methods at 273 K decreased with the evolution of gold species from high valence to low valence, no maximum of TOF was observed although gold particles in the catalyst attained to about 2-3 nm during the treatment. An Au/ceria catalyst with a gold load of 0.87% （mass fraction） maintained a good activity for CO oxidation within 18 h at room temperature. The catalysts were characterized via transmitted electronic microscopy（TEM）, inductively coupled plasma optical emission spectrometry（ICP-OES）, X-ray diffraction（XRD） and BET specific surface area and UV-Vis DRS as well.

Gold-iridium bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions

Carbon supported gold-iridium composite(Au Ir/C) was synthesized by a facile one-step process and was investigated as the bifunctional catalyst for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). The physical properties of the Au Ir/C composite were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS). Although the Au and Ir in the Au Ir/C did not form alloy, it is clear that the introduction of Ir decreases the average Au particle size to 4.2 nm compared to that in the Au/C(10.1 nm). By systematical analysis on chemical state of metal surface via XPS and the electrochemical results, it was found that the Au surface for the Au/C can be activated by potential cycling from 0.12 V to 1.72 V, resulting in the increased surface roughness of Au,thus improving the ORR activity. By the same potential cycling, the Ir surface of the Ir/C was irreversibly oxidized, leading to degraded ORR activity but uninfluenced OER activity. For the Au Ir/C, Ir protects Au against being oxidized due to the lower electronegativity of Ir. Combining the advantages of Au and Ir in catalyzing ORR and OER, the Au Ir/C catalyst displays an enhanced catalytic activity to the ORR and a comparable OER activity. In the 50-cycle accelerated aging test for the ORR and OER, the Au Ir/C displayed a satisfied stability, suggesting that the Au Ir/C catalyst is a potential bifunctional catalyst for the oxygen electrode.

Promoter effect of La2O3 on gold catalyst with different textural structures

Silica supported gold nanoparticles were synthesized and promoted by lanthanum oxide as dopant. The influences of LaOand silica textural structure on the gold dispersion, formation of active species, crystalline composition and the reacting role of dopants were studied in detail. The characterization results suggested that the dispersion of gold nanoparticles depended on the textural structure of silica without lanthanum oxide doping where small mesopores are more preferable to disperse gold nanoparticles. The addition of lanthanum oxide largely increased the dispersion of gold nanoparticles and oxygen active sites independent of the textural structure of silica support. The interaction between lanthanum oxide and silica enhanced by the synergy facilitated the release of oxygen vacancies and transition of active oxygen species. In addition, the chemical properties were greatly changed after lanthanum oxide addition which was only inconspicuously impacted by the initial textural structure of silica supports, shedding light on the further design of economic gold catalyst based on simple synthesis method.

Deactivation studies of nano-structured iron catalyst in Fischer-Tropsch synthesis

A nano-structured iron catalyst for syngas conversion to hydrocarbons in Fischer-Tropsch synthesis（FTS） was prepared by micro-emulsion method.Compositions of bulk iron phase and phase transformations of carbonaceous species during catalyst deactivation in FTS reaction were characterized by temperature-programmed surface reaction with hydrogen（TPSR-H 2 ）,and XRD techniques.Many carbonaceous species on surface and bulk of the nano-structured iron catalysts were completely identified by combined TPSR-H 2 and XRD spectra and which were compared with those recorded on conventional co-precipitated iron catalyst.The results reveal that the catalyst deactivation results from the formation of inactive carbide phases and surface carbonaceous species like graphite,and it will be increased when the particle size of iron oxides was reduced in FTS iron catalyst.

Halloysite Nanotubes Supported Gold Catalyst for Cyclohexene Oxidation with Molecular Oxygen

The selective oxidation of cyclohexene to 2-cyclohexene-1-ol and 2-cyclohexene-1-one has been investi-gated over Au/HNTs (HNTs: halloysite nanotubes) catalysts with molecular oxygen in a solvent-free system. The catalysts were prepared by deposition precipitation method and characterized by ICP-AES, TEM and XRD. The results show that the catalytic performance of Au/HNTs is quite well and the catalytic activity over recycled catalyst remains highly. Moreover, the nano-size effect of gold is also reported for the reaction.

Gold Catalysts Supported on Crystalline Fe_2O_3 and CeO_2/Fe_2O_3 for Low-temperature CO Oxidation

High active and stable gold catalysts supported on crystalline Fe203 and CeO2/Fe2O3 were prepared via the deposition-precipitation method. The catalyst with a Au load of 1.0% calcined at 180 ℃ showed a CO conversion of 100% at -8.9℃, while Au/CeO2/Fe2O3 converted CO completely at -16.1 ℃. Even having been calcined at 500 ℃, Au/Fe2O3 still exhibited significant catalytic activity, achieving full conversion of CO at 61.6℃. The catalyst with a low Au load of 0.5% could convert CO completely at room temperature and kept the activity unchanged for at least 150 h. N2 adsorption-desorption measurements show that the crystalline supports possessed a high specific surface area of about 200 m2/g. Characterizations of X-ray diffraction and transmission electron microscopy indicate that gold species were highly dispersed as nano or sub-nano particles on the supports. Even after the catalyst was calcined at 500 ℃, the Au particles remained in a nano-size of about 6--10 nm. X-ray photoelectron spectra reveal that the supported Au existed in metallic state Au0. The modification of Au/Fe2O3 by CeO2 proved to be beneficial to the inhibition of crystallization of Fe2O3 and the stabilization of gold particles in dispersed state, consequently promoting catalytic activity.

In situ IR, pulse reaction and TPD-ITD study of catalytic performance of room-temperature carbon monoxide oxidation on supported gold catalysts

With in situ IR, two different CO adsorption bands were detected on various chemical state gold catalysts. One band is attributed to the linear CO on an oxidized gold catalyst(2100 cm -1 ), the other one is ascribed to the bridged CO on metallic gold (2085 cm -1 ). CO pulse reaction showed that Au/Fe 2O 3 catalyst had a room temperature activity even in the presence of moisture. The produced CO 2 was detained and more easily desorbed from supported gold catalyst than support oxide. TPD IDT results indicated that the O - 2 superoxide ions are the possible active oxygen species.

THE SUPPORTED GOLD CATALYSTS FOR CLOSED CYCLE CO_2 LASER

Sealed-off carbon dioxide lasers encounter problem of dissociation of CO2, Which causes the output power to fall. Reformation of CO2 is therefore essential for long life CO2 lasers. Au/Fe2O3 and Au/NiFe2O4 are promising candidates for this application.

PEO-b-P4VP/Yttrium Hydroxide Hybrid Nanotubes as Supporter for Catalyst Gold Nanoparticles

吸附(乙烯氧化物) poly， -b-poly(4-vinylpyridine)(PEO-b-P4VP) 微粒与稠密的 P4VP 内部层和包围 YNT 的拉长的 PEO 外部层导致了到钇氢氧化物 nanotubes (YNT ) 的表面上混合 nanotubes。稠密的 P4VP 层被 crosslinking 进一步作为 crosslinker 用 1,4-dibromobutane 稳定。然后， crosslinked 混血儿 nanotubes (CHNT ) 作为一个新奇 nano 支持者被使用在 crosslinked P4VP 层以内装载催化剂金牌 nanoparticles (GNP ) 。结果的 GNPs/CHNTs (在 CHNT 上装载的 GNT ) 被使用催化 p-nitrophenol 的减小反应。结果显示这个新奇 nano 支持者在暂停，在装载 GNP (0.87 mmol/g ) 的高能力，装载 GNP (12.9 mol1min1 ) 的高催化的活动，和 GNTs/CHNTs 的好可重用性有象好 dispersity 那样的优点。

In situ modification of heavy oil catalyzed by nanosized metal-organic framework at mild temperature and its mechanism

Two catalysts, nano-sized cobalt-metal-organic framework(Co-MOF) and nickel(Ni)-MOF, were successfully prepared by the modification method. Tetralin(C10H12) was used as the hydrogen donor for the catalytic cracking and hydrogenation modification study of the dehydrated crude oil from the Shengli Oilfield. The optimal reaction conditions were determined through orthogonal experiments, and the components of the crude oil and modified oil samples were analyzed. The results revealed that the nanoMOF catalysts were successfully prepared and exhibited high catalytic activity. They could catalyze the cracking of large molecules in heavy oil at mild temperatures(<300°C), leading to the decomposition of the hydrogen donor. When the mass fraction of the catalyst was 0.2%, the mass fraction of the hydrogen donor was 1%, and the reaction temperature was 280°C, the Ni-MOF showed the best catalytic viscosity reduction effect. It could reduce the viscosity of heavy oil at 50°C from 15761.9 m Pa.s to 1266.2 m Pa.s,with a viscosity reduction rate of 91.97%. The modification effect of Co-MOF was the next best, which could reduce the viscosity of heavy oil to 2500.1 m Pa.s with a viscosity reduction rate of 84.14%. Molecular dynamics simulations revealed a strong interaction force between the MOF surface and asphaltene molecules. In the process of heavy-oil catalytic hydrogenation, the nano-MOF catalyst exhibited high catalytic activity. On the one hand, the empty d orbitals outside the metal atoms in the catalyst could polarize the carbon atoms in the organic matter, accelerating the breaking of long chains. On the other hand, the metal atoms in the catalyst could bond with the carbon σ bonds, breaking the carbon-carbon bonds. This disrupted the structure of the recombined components in the crude oil, irreversibly reducing the viscosity of the heavy oil and improving its fluidity.

金催化乙炔氢氯化的密度泛函理论研究进展

乙炔氢氯化(AH)是生产氯乙烯的主要途径之一,传统上使用高毒性的汞催化剂,因此开发无汞催化剂迫在眉睫.金(Au)催化剂是最有潜力的替代催化剂之一,然而其活性Au物种、反应物的活化过程或反应过渡态结构等催化机理仍不够清晰.密度泛函理论(DFT)在研究由Au催化AH的反应机理中发挥了极其重要的作用.我们综述了DFT对金催化剂活性位点、反应物在催化剂上的吸附性质及反应机理的研究进展.重点讨论了DFT对阳离子金和金簇催化AH反应过程的模拟计算,包括Au电子状态、其它原子掺杂及金簇尺寸和形状对催化AH反应影响的模拟.结果表明DFT模拟计算在微观分子尺度上研究反应物的吸附、反应中间体及过渡态等方面发挥了关键作用,对理解Au催化AH反应机理做出了重要贡献.

Fe@CeO_(2)/CN双空腔核壳磁性载金椭球催化剂及其催化还原对硝基苯酚和染料污染物

载金催化剂可在温和条件下还原性降解环境中某些有毒有害污染物,并转化为低毒性、高附加值的物质,从而促进水体污染物化学资源转化和综合利用.本文设计制备Fe@CeO_(2)/CN双空腔核壳磁性载金椭球催化剂,用于还原降解水体中对硝基苯酚和染料污染物.该催化剂先制备Fe_(2)O_(3)@CeO_(2)梭型微粒内核,采用乙二胺介导的Stober扩展法在其表面合成SiO_(2)@RF复合物,经过碳化-水热蚀刻得到具有介孔碳氮壳层的Fe_(2)O_(3)@CeO_(2)/CN椭球;采用[Au(en)_(2)]^(3+)为金前驱体的沉积沉淀-还原气氛热处理法在上述椭球中构筑较好分散度超细纳米Au颗粒,同时Fe_(2)O_(3)转化为小体积Fe颗粒并形成内空腔,得到Fe@CeO_(2)-Au/CN双空腔核壳磁性椭球催化剂.该催化剂独特的结构特征和复合组分协同增强性效应使其在还原降解对硝基苯酚和染料污染物中均表现优越的催化反应性能和循环使用性能,重复多次使用后仍保存良好的磁分离性和较好的结构完整性.

无汞催化合成氯乙烯工业化试验装置运行总结

介绍了金基无汞催化合成氯乙烯的工艺流程和工业化试验装置的运行情况,重点讨论了乙炔空速、反应温度和运行时间对乙炔转化率的影响,并对比了无汞催化剂和低汞催化剂的使用条件和经济性。

废金催化剂中提取金的工艺研究

随着石油化工以及有机合成工业领域的发展,黄金催化剂的需求量日益增加。从废金催化剂中高效地回收黄金,不但降低了催化剂的使用成本,而且满足国家绿色发展的环保观念。因此,实现黄金的高效回收,具有十分重要的作用和意义。本文介绍了一种高效便捷的黄金回收工艺,具有回收率高,操作简便,生产成本低等特点,有较高的工业推广价值。

Preparation of Au/CeO_2 catalyst and its catalytic performance for HCHO oxidation

Aqueous precipitation and deposition-precipitation method were used to prepare CeO2 supports and Au/CeO2 catalysts, respectively. The effect of preparation condition of support on the catalyst activity was investigated. The catalytic combustion of HCHO was considered as the probe reaction for comparing the catalyst activity. The BET, X-ray diffraction, X-ray photoelectron spectroscopy （XPS）, and reduction （TPR） were carried out to analyze the influence factor on the catalysts activity. The results showed that the addition of dispersant and use of microwave in the support preparation procedure could be beneficial for enhancing the interaction of supports and gold species and thus improved the catalytic activity. The total conversion temperature for HCHO was 146 ℃ over AC400. With the modification during supports preparation process, the catalytic activity increased with total conversion temperature decreasing to 98 ℃. The results of XPS indicated that Au^0 and Au^＋1 species coexisted in these catalysts and the activity of catalyst correlated with Au^＋1/Au^0 ratio. Temperature-programmed reduction results demonstrated that the reduction peak appeared between 100-170 ℃ with the inducing of gold. The dependence of activity on the reduction peak temperature implied that ionic gold was catalytic activity component for HCHO oxidation.