氨合成塔使用预还原氨合成催化剂的探讨

预还原氨合成催化剂为制造厂预先将催化剂还原好并进行表面钝化处理等,合成氨厂使用时只需将其表面的钝化部分经简单再还原即可;而传统合成氨生产中使用的氧化态氨合成催化剂并无预先还原的过程,需在氨合成塔内进行整个还原过程。为探究氧化态氨合成催化剂与预还原氨合成催化剂的优劣,从两者的装填、还原过程、活性以及经济性等方面进行对比分析,认为氧化态氨合成催化剂装填较为容易,其还原更需严格控制好各项工艺参数,还原后与预还原氨合成催化剂的活性相差不大;而预还原氨合成催化剂装填需小心谨慎和做好保护等,可明显缩短系统开车时间,节约开车成本,具有明显的经济效益。小型合成氨装置建议使用氧化态氨合成催化剂,大中型合成氨装置推荐全部或部分使用预还原氨合成催化剂。     

制备与使用条件对中变催化剂性能的影响

本文讨论了铁铬系中变催化剂在空气升温过程中超温现象的原因、制备过程中残存低价铁与高价铬对催化剂性能的影响以及提高铁铬系催化剂还原态强度的途径。     

XA201-H-1型还原态催化剂的制备和工业应用

简要分析了氨合成催化剂在合成氨生产装置中直接还原存在的问题,概述了XA201-H-1型还原态催化剂的特性、制备、装填过程及其注意事项。该还原态催化剂在氨合成装置中的实际应用情况表明:还原态催化剂直接升温至起活温度后,短期内即能满负荷生产,可缩短开车时间和节省开车费用,特别适合于少量更换催化剂的情况。     

多组元贵金属尾气净化催化剂的氧化性能

用微反装置研究了Pt-Pd/Al₂O₃和Pt-Rh-Pd/Al₂O₃催化剂氧化态和还原态的催化活性。对催化剂进行了XRD、TPD和TPR表征,并对反应机理进行了探讨。结果表明,氧化态Pt-Pd/Al₂O₃催化剂的氧化性能优于其还原态,且具有相同的催化机理;氧化态Pt-Rh-Pd/Al₂O₃催化剂的氧化性能逊于其还原态,主要是由不同的催化机理所致。     

B113型变换催化剂的不钝化法部分更换及还原

介绍了重油制氢装置中还原态CO变换催化剂部分更换技术以及实施过程中采取的处理措施 ,探讨了其风险性 ,对其技术经济进行了对比     

还原空速对Fe/Cu/K/SiO2催化剂浆态床F-T合成性能的影响

在浆态床反应器中详细考察了合成气还原空速对微球状工业铁基催化剂还原和反应后的物相以及F-T合成反应性能的影响. 研究结果表明：空速能够影响铁基催化剂还原反应进程，催化剂在较高的空速下易被还原，还原后催化剂的比表面积降低，平均孔径增大. 在较低空速下还原时，还原形成的高的CO₂分压对铁物相有一定的氧化作用，使得还原态催化剂中的Fe³⁺(spm)含量增大. 还原空速对F-T合成烃产物分布影响不明显，但对催化剂的反应活性和运行稳定性影响较大，较低和较高空速还原后的催化剂失活速率均较高，适宜的还原空速为1.0～2.0 L•（g cat）^-1•h^-1.     

Ф2200mm氨合成系统更换还原态催化剂总结

简述了Ф2200mm氨合成塔部分更换还原态催化剂过程及使用效果。更换催化剂后，合成系统压力降低2MPa，甲烷含量提高2％（体积分数），液氨产量提高20t／d，运行情况明显改善。     

还原参数对铁基催化剂F—T合成性能的影响

在浆态床反应器中详细考察了还原参数对工业铁基催化剂在F—T合成反应中的影响。研究结果表明：提高还原气体中CO／H2的比值有助于提高烯烃的选择性;提高还原气体的空速可以提高催化剂的活性,但是烯烃的选择性有所降低;升高还原温度在一定程度上可以提高催化剂的活性,但是温度过高容易造成催化剂积炭活性下降,适宜的还原温度范围为210～260℃。     

还原态氨合成催化剂的应用

沧州正元化肥有限公司JRφ3000氨合成塔,全塔采用还原态催化剂。从氨合成工段正式点火升温,到产出合格液氨产品共用15h,大大缩短了升温还原时间,为企业节省了可观的开车费用。     

结构化铜基催化剂电化学还原CO2为多碳产物研究进展

近年来,随着有关铜基催化剂价态、晶面、微观形态等结构化因素对其催化性能影响的研究不断深入,铜基催化剂电化学还原CO₂高选择性制备高附加值多碳（C₂₊）产物取得长足进展。本文系统综述了近五年来结构化铜基催化剂电化学还原CO₂生成C₂₊产物的研究报道,并分析总结了铜基催化剂表面混合价态、高活性晶面和丰富晶界的存在,以及富含限域空间的形态学结构（纳米线阵列、纳米树突和纳米多孔结构等）的构建与其电化学还原CO₂生成C₂₊产物的活性和选择性之间的构效关系。进一步提出了CO₂电化学还原领域发展的新趋势,即充分发挥各个结构化因素的协同作用,原位制备具有混合价态和丰富晶界的纳米多孔结构铜基催化剂,并在流通池中高效还原CO₂持续生成C₂₊产物。     

B205-1型低变催化剂在建峰化肥厂的应用

介绍B205-1型低变催化剂在布朗工艺合成氨装置上的应用情况,运行结果表明催化剂具有易还原、活性好、强度高、抗毒性强等特点.     

LK-821-2型低变催化剂的应用

介绍了LSK型低变保护剂和LK-821-2型低变催化剂装填和升温还原情况以及在高串低变换流程中的应用。该催化剂的成功应用,降低了下游脱碳系统溶液维护成本,降低了工艺冷凝液系统设备的腐蚀速率,日增产合成氨约10t、尿素7～9t。     

Development of a hybrid catalytic combustor for a 1300°C class gas turbine

The hybrid catalytic combustor concept proposed by the authors has an advantage concerned with catalyst durability, because the catalyst is maintained below 1000°C even for application to 1300°C class gas turbines. A full-scale hybrid catalytic combustor has been designed for a 200 MW (1300°C) class gas turbine. The catalyst bed was 450 mm in diameter and consisted of a Pd/ alumina washcoat on a cordierite monolith. In experiments, the combustor has demonstrated the capability of meeting the NO_x emission level of SCR (selected catalytic reduction) during atmospheric pressure testing. To predict the catalyst performance at an elevated pressure, the characteristics of the catalyst were studied using a small scale reactor test, and a material property test using a DTA/TGA-Q.MASS system. The catalyst showed a higher activity in the oxidized state (PdO) than in the metallic state (Pd). This activity difference was governed by the equilibrium of the oxygen release from PdO in bulk. It was considered that oxidation rate of the metallic Pd in bulk was not so high and this caused self-oscillation for the Pd catalyst around the temperature of the oxygen release equilibrium. Even below the temperature of the oxygen release equilibrium, both surface and bulk (lattice) oxygen of the PdO was consumed by the methane oxidation reaction, and resulted in a lack of surface oxygen on the catalyst. This caused a reversible decrease in the catalyst activity during combustion testing, and indicated that the oxygen dissociation step was a rate limiting step in the catalytic combustion.     

Active state of model cobalt foil catalyst studied by SEM, TPR/TPO, XPS and TG

Four states of the cobalt foil catalyst, corresponding to different redox treatment and activity, were defined: oxidised, reduced, active and deactivated. They were investigated by scanning electron microscopy (SEM), temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS) and thermogravimetric (TG) methods and in the hydrogenation of ethylene used as a test reaction. Particular emphasis was laid on the study of the active state, achieved after the catalyst reduction at moderate temperatures. It was shown that the catalyst preactivated by a series of redox cycles is built of a cobalt oxide layer of a characteristic size and dispersion, which is stuck to the metallic bulk. Reduction at a moderate temperature, prolonged even to several hours, converts only a small fraction of the oxide layer into metallic Co. XPS, TPR and TPO methods distinguished various states of oxygen and cobalt on the surface of the activated or partially activated samples. The results were interpreted in terms of the mechanism of autocatalytic reduction. The deactivation was associated with the structural reconstruction of the surface, taking place either in the reaction mixture during the hydrogenation of ethylene or in hydrogen atmosphere. Formation of the inactive carbon deposit was experimentally excluded.     

NO–NH3 coadsorption on vanadia/titania catalysts: determination of the reduction degree of vanadium

Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) has been used to study NH₃ and NO adsorption over a 15% w/w vanadia/titania catalyst. NH₃ is adsorbed as coordinate NH₃ and NH₄⁺ species over the oxidised catalyst, leading to the reduction of the vanadia surface. At 300°C, adsorbed nitrosyls species are detected, suggesting that the oxidation of gaseous or adsorbed ammonia species takes place over the V=O sites. Coadsorption experiments show that NO is able to reoxidise about the 57% of the reduced V=O groups, resulting in N₂, according to a NO+V_□→1/2N₂+V=O reaction. On the other hand, NO is only adsorbed over vanadia reduced surfaces. The measure of the area of the 2ν(V=O) bands results in an estimate of the oxidation state of vanadium. From this estimate it can be concluded that nitrosyls species are adsorbed on the catalyst surface for vanadium atoms having an oxidation state ranging from +4 to +3.1.     

A301型氨合成催化剂应用小结

总结了A301型低温、低压、高活性氨合成催化剂在Φ1 800 mm合成塔的实际应用情况。介绍了合成系统的配置、工艺流程以及催化剂的装填情况,通过催化剂升温还原状况和生产过程运行数据的比较,对A301型氨合成催化剂的应用效果进行了评价,充分反映出A301型氨合成催化剂活性高、使用压力低、氨产量大等优良的性能特点。     

Cracking of n-dodecane during supercritical state on HZSM-5 membranes

In the new generation of aircraft, jet fuel will serve as both an energy source and a heat sink for cooling through endothermic fuel reactions. Catalytic cracking of hydrocarbon fuel has proved to be potential for endothermic reaction. For this application, we have prepared ZSM-5 membranes as catalyst on the surface of stainless steel by secondary growth method. An optimized activation procedure of ZSM-5 membrane for catalytic cracking reaction is established by combining the results of catalytic reaction with thermal analysis (TGA and DSC). Taking n-dodecane as a model compound, the influence of silica alumina ratio (SAR = nSiO₂/Al₂O₃) of initial gel on the activity of hydrocarbon cracking reaction were studied. The results also demonstrate that the conversion of catalytic cracking reaction is much higher than that of pyrolysis during supercritical state. In addition, hydrogen molar ratio in gas production decreases with increasing the reaction temperature. Besides that, the optimum temperature for coke removal and the reduction of zeolite catalysts is between 550 °C and 600 °C.     

NC74-1型氨合成催化剂的升温还原及应用

介绍了NC74-1氨合成催化剂在山东华鲁恒升化工股份有限公司大氮肥氨合成的装填、升温还原及使用情况。