Fe2O3-CuO/ZSM-5催化剂催化低浓度瓦斯制甲醇

采用催化氧化的方法,将煤矿抽采瓦斯制成高价值的化学品或液体燃料甲醇是其综合利用的一个发展方向。寻找对瓦斯转化具有较好的催化效果,且能替代贵金属催化剂的普通催化剂是瓦斯催化氧化制甲醇的研究重点。本文以硝酸铁、硝酸铜和ZSM-5分子筛为原料,采用离子交换法制备了Fe₂O₃/ZSM-5、CuO/ZSM-5和Fe₂O₃-CuO/ZSM-5催化剂,并在乙酸溶剂中考察了3种催化剂催化低浓度瓦斯部分氧化合成甲醇的性能。结果表明,Fe₂O₃/ZSM-5、CuO/ZSM-5和Fe₂O₃-CuO/ZSM-5对瓦斯部分氧化制甲醇反应均有催化活性,但Fe₂O₃-CuO/ZSM-5的催化效果最明显,且Fe、Cu负载量对催化剂的催化活性影响较为显著,Fe和Cu的最佳理论负载量分别为4.21%和3.22%。在Fe₂O₃-CuO/ZSM-5(x_Fe=4.21%,x_Cu=3.22%)添加量为0.1g、乙酸溶剂用量30mL的条件下,Fe₂O₃-CuO/ZSM-5催化甲烷体积分数为20%配制瓦斯制甲醇的最佳反应条件为初始反应压力4.0MPa、反应温度200℃、反应时间3h。     

Pd/NaY催化苯甲醇无溶剂选择性氧化反应

采用离子交换法将[Pd(NH₃)₄]²⁺交换到NaY分子筛中,经焙烧和氢气还原制备金属钯粒径可调变的Pd/NaY催化剂。在(120~500) ℃改变焙烧温度,可以获得金属钯粒径(1.3~11.9) nm的Pd/NaY催化剂。Pd/NaY催化剂能够催化苯甲醇的无溶剂选择性氧化反应,对含不同钯粒径的Pd/NaY催化剂上醇选择性氧化研究发现,在1.6%Pd/NaY催化剂用量0.1 g、反应温度100 ℃、苯甲醇用量48.5 mmol和O₂流速3 mL·min^-1条件下,苯甲醇转化的真实转化频率随粒径变化在3.2 nm处呈最大值,该反应为结构敏感反应。     

N掺杂石墨制备高热稳定性甲醇合成催化剂

Cu-ZnO-Al₂O₃甲醇合成催化剂结构中具有不同的功能组分,其中Cu是活性组分,ZnO协同Cu组分进行催化,Al₂O₃作为载体稳定各活性中心,C作为脱模剂用于催化剂颗粒定型打片。对催化剂的C组分进行N掺杂,并利用其改性了甲醇合成催化剂。改性后的催化剂具有介孔扩充、粒径减小、活性组分协同作用增强的优点,可以催化合成气转化为甲醇,并且在保持甚至高于之前催化活性的前提下将耐热后活性衰退率降低约33%。通过该处理方法,将C组分的作用由脱模剂转变为助剂,使其参与到催化反应中,提高了甲醇合成催化剂的高热稳定性。     

改性钒铈基催化剂催化氧化烟气中邻二甲苯

燃煤过程中产生微量VOCs随烟气排放将导致大气污染。本文以Mn、Fe、Co、Cu对钒铈钛（Ce-V₂O₅/TiO₂）催化剂进行改性,并研究催化剂对烟气中典型VOCs中的邻二甲苯氧化脱除行为。研究结果表明,Mn、Fe改性分别在低温段和中高温段有效提高Ce-V₂O₅/TiO₂催化剂对烟气中邻二甲苯的催化氧化效率。烟气中的水蒸气、SO₂、NH₃、NO对催化氧化有不同的抑制程度,其中NH₃对催化效率抑制作用最强。不同改性催化剂对烟气组分反应不同,Fe改性Ce-V₂O₅/TiO₂催化剂抗烟气复杂组分中抗毒性最强。表征结果表明,Fe改性的Ce-V₂O₅/TiO₂催化剂表面积高、氧化还原性强,具有高催化活性与较强抗中毒性,可能成为一种针对燃煤烟气中有机污染物高效脱除的有潜力的催化剂材料。     

富氧条件下金属催化CO还原NO的研究进展

CO广泛存在于燃煤烟气及汽车尾气中,利用未完全燃烧的CO催化还原NO可同时脱除NO和CO,过程中催化剂起着决定性作用。本文对近年来含氧条件下CO催化还原NO的研究成果进行了系统梳理,重点关注了Pd系、Ir系、Cu系、其他贵金属及金属氧化物催化剂的研究进展,分析了催化剂制备方法、掺杂改性及反应条件对催化性能的影响,同时考察了O₂浓度、H₂O以及SO₂对催化反应的影响,总结并对比了不同体系催化剂的活性位点及其催化机理,指明了O₂在催化还原过程中的抑制机理,得出了几种体系催化剂催化CO还原NO的活性顺序。最后,针对富氧条件下CO催化还原NO所存在的问题和难点,提出深入研究O₂抑制机理、降低贵金属用量、添加活性助剂是今后的研究方向。     

富氢气体中CO优先氧化催化剂研究进展

以高纯氢为燃料的质子交换膜燃料电池广泛应用于电动汽车,但其阳极容易被富氢气体中含有的少量CO毒化,造成电池性能严重降低。富氢气体在进入燃料电池前,必须进行CO净化处理。优先氧化法是除去富氢气体中少量CO最简单经济有效的方法,常用催化剂主要有Pt系、Au系和Cu系催化剂。着重阐述负载Au催化剂的制备方法、载体调变、助剂改性以及其他因素（如反应气氛中CO与O₂浓度比、水蒸汽和CO₂等）对Au催化剂CO优先氧化反应催化性能的影响。介绍以CuO/CeO₂催化剂为典型的非贵金属氧化物催化剂用于CO优先氧化反应的研究成果以及制备方法、载体和助剂改性等对催化性能的影响和反相结构CeO₂/CuO的催化性能。考虑利用催化剂活性组分,尤其是Au与Cu之间的协同作用,选用合适的载体,进行催化剂组分的设计仍然是今后研究的热点。突破常规无定形金属氧化物作载体,通过设计合成具有特定形貌的载体,研究不同晶面和不同价态等因素对催化剂CO优先氧化催化性能的影响,也是一项很有意义的研究。     

二氧化碳甲烷化催化剂及反应机理研究进展

在“双碳”目标的背景下，明确碳处理路径至关重要。利用可再生能源制得的氢，将二氧化碳(CO₂)通过甲烷化反应制备合成天然气(SNG)被广泛认为是一种高效、有前景的碳捕集利用技术，有望实现碳循环利用。近年来，二氧化碳甲烷化催化剂及相关反应机理均取得了许多新进展。鉴于此，本工作对该反应进行了系统的综述。首先，介绍了CO₂甲烷化反应的热力学研究中不同反应条件的影响；随后从活性金属、载体、制备方法及辅助技术等四方面介绍了CO₂甲烷化催化剂的研究进展，其中活性组分包括非贵金属基(Ni,Fe,Co和Mo)和贵金属基(Ru,Rh,Pt和Pd)，载体包括传统氧化物(Al₂O₃,SiO₂,TiO₂,ZrO₂和CeO₂)和新型载体材料(金属有机框架和碳基材料)，催化剂制备方法包括传统制备方法(浸渍法、共沉淀法、水热法、溶胶-凝胶法和固相合成法)和合成辅助技术(超声波、微波和等离子体等)；总结了CO₂     

二氧化碳与不饱和烃制备丙烯酸及其衍生物研究进展

CO₂高值转化是“双碳”目标大背景下碳利用的有效方式。过渡金属络合物催化的CO₂与不饱和烃羧化反应是合成丙烯酸及其衍生物的新路线,也是CO₂高值利用的新途径。本文总结了多种金属络合物（Ni、Pd、Cu等）在催化CO₂与烯烃偶联羧化、CO₂与炔烃或联烯还原羧化制丙烯酸及其衍生物中的应用,着重概述了不同催化体系中的金属-配体优化和反应条件调控,系统对比了不同催化剂的催化特点和作用机制,并论述了其催化反应循环中的控速步骤以及催化剂再生等关键问题。最后,对过渡金属络合物催化CO₂与乙烯偶联羧化制备丙烯酸及CO₂与炔烃或联烯还原羧化合成高区域选择性不饱和羧酸衍生物的后续研究方向和应用前景进行了展望。     

非贵金属改性钒钛基催化剂NH3-SCR脱硝协同控制VOCs

在钒钛基催化剂上分别负载四种非贵金属(Ce、Cu、Mn、Fe)，研究改性催化剂对中低温选择性催化还原(SCR)脱硝协同挥发性有机物(VOCs)催化氧化的性能。对四种负载金属(Ce、Cu、Mn、Fe)分别进行SCR脱硝和VOCs催化氧化，发现Ce改性的催化剂在低温段具有良好的SCR脱硝活性和VOCs催化氧化性能，被认为具有良好的协同催化潜力。之后对Ce掺杂改性催化剂进行协同评价研究，发现在275～300℃的温度区间内，3V-5Ce/Ti催化剂的NO转化率和VOCs转化率可达到100%。并分别比较了SCR反应协同VOC与未协同VOC时N₂的选择性和CO₂的选择性，发现在低温段时甲苯的引入会显著降低N₂选择性，而随着温度升高，N₂O副产物的产生，N₂的选择性恢复到未引入甲苯时。同时发现协同反应时CO2的选择性有明显下降。对3V-5Ce/Ti催化剂的SEM、XRD、XPS、NH3-TPD表征说明Ce的引入不会破坏载体形貌，可以为催化剂提高更多表面氧空位，从而提高催化剂的氧化还原性能，并...     

Pd-Co/CNT复合催化剂的制备及甲醇电氧化性能

以Pd Cl₂和Co(NO₃)₂为原料，采用分步乙二醇还原法制备了多壁碳纳米管负载Pd-Co复合纳米催化剂Pd-Co/CNT。利用TEM、XRD和XPS对催化剂的结构进行了表征，考察了其甲醇电氧化性能。结果显示，Co的引入使Pd催化剂的分散性得到改善，其电化学表面积可达39.7 m²/g。循环伏安测试表明，当Pd∶Co物质的量比为1∶0.2时，Pd-Co/CNT的甲醇氧化峰电流密度约为Pd/CNT的2.7倍。计时电流结果表明，Co的添加使催化剂的活性衰减比例由Pd/CNT的63.8%降至54.2%，显示出较强的抗中毒能力。Pd-Co复合催化剂性能的改善归因于Pd与Co之间的协同相互作用。     

Catalytic combustion of methane over supported bimetallic Pd catalysts: Effects of Ru or Rh addition

A series of Pd/γ-Al₂O₃ catalysts with various amounts of Ru or Rh with, and/or without, BaO were prepared by successive incipient wetness impregnation. The catalysts were investigated for the catalytic methane combustion before, and after, H₂S poisoning in an oxygen-rich atmosphere. The addition of ruthenium enhanced the catalytic activity for methane oxidation even after H₂S poisoning while maintaining the initial catalytic activity of the fresh catalyst. These results are explained in terms of dispersion of palladium by ruthenium and poisoning resistance of ruthenium. The addition of rhodium did not improve the overall activity in methane oxidation.     

Catalytic combustion of methane over bimetallic catalysts a comparison between a novel annular reactor and a high-pressure reactor

The effects of adding a co-metal, Pt or Rh, to Pd/γ-Al₂O₃ catalysts were studied with respect to the catalytic activity for methane combustion and compared to a Pd/γ-Al₂O₃ catalyst, using both a pressurized pilot-scale and a lab-scale annular reactor. Temperature programmed oxidation (TPO) experiments were also carried out to investigate the oxygen release/uptake of the catalyst materials. Palladium showed an unstable behavior both in the pilot and lab-scale experiments at temperatures well below the PdO to Pd transformation. An addition of Pt to Pd stabilized, and in some cases increased, the catalytic activity for methane combustion.

The TPO experiments showed that the oxygen release peak was shifted to lower temperatures even for low additions of Pt, i.e. Pd:Pt=2:1. For additions of rhodium only small beneficial effects were seen. The steady-state behavior of the lab-scale annular reactor correspond well to the pressurized pilot-scale tests.     

Catalytic combustion of methane over bimetallic Pd–Pt catalysts: The influence of support materials

The effect of support material on the catalytic performance for methane combustion has been studied for bimetallic palladium–platinum catalysts and compared with a monometallic palladium catalyst on alumina. The catalytic activities of the various catalysts were measured in a tubular reactor, in which both the activity and stability of methane conversion were monitored. In addition, all catalysts were analysed by temperature-programmed oxidation and in situ XRD operating at high temperatures in order to study the oxidation/reduction properties.

The activity of the monometallic palladium catalyst decreases under steady-state conditions, even at a temperature as low as 470 °C. In situ XRD results showed that no decomposition of bulk PdO into metallic palladium occurred at temperatures below 800 °C. Hence, the reason for the drop in activity is probably not connected to the bulk PdO decomposition.

All Pd–Pt catalysts, independently of the support, have considerably more stable methane conversion than the monometallic palladium catalyst. However, dissimilarities in activity and ability to reoxidise PdO were observed for the various support materials. Pd–Pt supported on Al₂O₃ was the most active catalyst in the low-temperature region, Pd–Pt supported on ceria-stabilised ZrO₂ was the most active between 620 and 800 °C, whereas Pd–Pt supported on LaMnAl₁₁O₁₉ was superior for temperatures above 800 °C. The ability to reoxidise metallic Pd into PdO was observed to vary between the supports. The alumina sample showed a very slow reoxidation, whereas ceria-stabilised ZrO₂ was clearly faster.     

Methane oxybromination over Rh-based catalysts: Effect of supports

Bromine mediation has been regarded as one of the most efficient ways to activate and convert methane to useful organics. This article reports the effects of active components (Rh, Ru, Pd and Pt) and supports (SiO₂, MgO and Al₂O₃) on the catalysis of methane oxybromination. Among the prepared catalysts, Rh/SiO₂ is the best in performance (CH₄ conversion of ca. 20% and CH₃Br selectivity exceeding 70%). The results reveal that support type has a notable influence on the catalytic performance of Rh, especially on product distribution. The high selectivity to CH₃Br over Rh/SiO₂ is attributed to its low propensity for CH₃Br oxidation. It was found that Rh small in particle size shows high catalytic activity and CH₃Br selectivity. Although silicalite-1 zeolite suffers from a certain degree of structural damage due to the presence of high temperature steam, the use of silicalite-1 as support results in a performance comparable to that of Rh/SiO₂.     

Pd catalysts supported on silicon nitride for the combustion of methane: Influence of the crystalline and amorphous phases of the support and of the preparation method on the catalytic performances

Non-oxide refractory materials, such as silicon nitride having high thermal stability and thermal conductivity can be used as catalytic supports. The influence of the Si₃N₄ support nature and of the chemical compounds used for preparations on the physical-chemistry and catalytic properties of the palladium systems in the total oxidation of methane was investigated. A strong influence of the phase composition and the crystalline state of supports on the catalytic properties in the total oxidation of methane of the Pd catalysts was found. The activity of Pd catalysts increases with the -Si₃N₄ content and crystallization state of the support. The catalytic activity of Pd/-Si₃N₄ is also strongly affected by the preparation procedure. The Pd/-Si₃N₄ catalyst obtained by aqueous impregnation is less active and less stable. It was proposed that if water is used as an impregnation solvent, the surface acid-based properties of Si₃N₄ support and/or of the Pd active phase are irreversibly damaged. Pd supported on -Si₃N₄, prepared by impregnation of the Pd precursors in toluene solutions are found to be the most active and stable under reaction conditions.     

Potential of zeolite supported rhodium catalysts for the CO2 reforming of CH4

Zeolite Y supported rhodium catalysts were prepared by ion-exchange starting from an aqueous solution of [Rh[(NH₃)₅Cl]Cl₂·6H₂0]. Previous work in this laboratory had shown that this procedure results in a Rh dispersion of near 100%. The catalysts were tested for their activity in the CO₂ reforming of CH₄. They were found to combine extraordinary stability with high activity and selectivity. At 923 K, 90 mol-% of the CH₄ was converted giving a H₂/CO ratio near unity. A weight loading of 0.5 to 0.93% Rh gives the highest turnover frequencies. Thermodynamic equilibrium is reached near 873 K. With a given Rh loading, the zeolite supports are superior to amorphous supports and NaY is superior to the HY. No deactivation was observed in tests of 30 h time on stream at atmospheric pressure or after repeated thermal cycles. No coke deposition was detected by temperature programmed oxidation of used catalysts. Temperature programmed reduction indicates the presence of three discernible Rh species.     

Performance of alumina-supported noble metal catalysts for the combustion of trichloroethene at dry and wet conditions

The performance of four different alumina-supported noble metal catalysts (0.5% of Pd, Pt, Rh and Ru, respectively) for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h⁻¹) in air was studied in this work. Experiments were carried out at both dry and wet (20,000 ppm of H₂O) conditions. Catalysts were compared in terms of activity, selectivity for the different reaction products (CO₂, HCl, Cl₂, C₂Cl₄, CCl₄ and CHCl₃), and stability at reaction conditions.

As general trend, the activity of the catalysts decreases in the order Ru  Pd > Rh > Pt. Concerning to the effect of the water addition, no important effect on the catalyst activity was observed, except in the case of Pt, for which an increase of the catalytic activity was observed. Reaction mechanism (and hence product distribution) is very similar for Rh, Pd and Pt, being in these cases C₂Cl₄ the only organochlorinated by-product detected. In the case of Ru, the reaction mechanism seems to be quite different, CCl₄ and CHCl₃ being the main organic by-products.

Simple power-law kinetic expressions (first order on trichloroethene concentration for Pd, Rh and Ru, and zeroth order for Pt) provide fairly good fits for catalytic performance of the studied catalysts.

Finally, deactivation studies show that both formation of active metal chlorides (especially in the case of Rh) and fouling (especially for Pd and Pt) are the main deactivation causes.     

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。     

The selective catalytic reduction of nitrogen oxides by methane on noble metal-loaded sulfated zirconia

The selective catalytic reduction of NO_x by methane on noble metal-loaded sulfated zirconia (SZ) catalysts was studied. Ru, Rh, Pd, Ag, Ir, Pt, and Au-loaded sulfated zirconia catalysts were compared with the intact sulfated zirconia. For the NO–CH₄–O₂ reaction, Ru, Rh, Pd, Ir, and Pt showed promotion effect on NO_x reduction, while for the NO₂–CH₄–O₂ reaction, only Rh and Pd showed promotion effect. Over intact and Rh, Pd, Ag, and Au-loaded sulfated zirconia, NO_x conversion in NO₂–CH₄–O₂ reaction was significantly higher than that in NO–CH₄–O₂ reaction, while clear difference was not observed over Ru, Ir, and Pt-loaded sulfated zirconia. Comparison of [NO₂]/([NO]+[NO₂]) in the effluent gases in NO–O₂ and NO₂–O₂ reactions showed that Ru, Ir, and Pt has high activity for NO oxidation under the reaction conditions. These facts suggest that effects of these metals toward NO_x reduction by methane can be categorized into the following three groups: (i) low activity for NO oxidation to NO₂, and high activity for NO₂ reduction to N₂ (Pd, Rh); (ii) high activity for NO oxidation to NO₂, and low activity for NO₂ reduction to N₂ (Ru, Ir, Pt); (iii) low activity for both reactions (Ag, Au). To confirm these suggestions, combination of these metals were investigated on binary or physically-mixed catalysts. The combination of Pd or Rh with Pt or Ru gave high activity for the selective reduction of NO_x by methane.     

Generation of H2O2 from H2 and O2 over zeolite beta containing Pd and heterogenized organic compounds

The catalytic generation of H₂O₂ from H₂ and O₂ has been studied over zeolite beta-supported Pd and zeolite beta-adsorbed organic compounds such as 1,4-benzoquinone (BQ), hydroquinone (HQ), azobenzene (AB) and hydrazobenzene (HAB). According to catalytic results, zeolite beta-supported Pd catalysts display effective performance relative to those prepared from other types of zeolites reported and Pd-loaded zeolite beta-adsorbed HQ catalysts show enhanced activity compared to zeolite beta-supported Pd catalysts. In situ UV–Vis spectroscopic study indicates that HQ can readily be converted to BQ reversibly under H₂ and air inside zeolite beta only in the presence of Pd. The results suggest that HQ acts as a strong hydrogen transfer agent to promote the production of H₂O₂ from H₂ and O₂ in cooperation with a Pd catalyst. By contrast, adsorption of BQ, AB and HAB induces suppression of the catalytic properties of Pd/zeolite beta.