氨分解制氢催化剂改性研究进展

在氨分解制氢技术中催化剂的选取尤为重要,其组成、形貌结构、载体、助剂等均能影响催化剂活性发挥。本文综述了近几年国内外氨分解制氢催化剂的改性研究现状,对催化剂的形貌结构变化、不同载体的影响、助剂的添加、矿石及工业废品在氨分解中的应用进行了详细的介绍,指出有效发挥催化剂和载体、助剂等之间的协同作用,改善外部条件,对于实现氨分解制氢具有很好的潜在实用价值,进一步设计出低压、低温、高活性氨分解的新型催化剂,降低能量消耗是未来氨分解催化剂的研究方向。     

氨催化分解制备无COx的氢气催化剂研究进展

介绍了国内外氨催化分解催化剂的研究进展,评述了理想的活性组分、载体和助剂及其具有的一些规律;总结了氨催化分解的反应机理、氨催化分解的动力学模型,认为氨N—H断裂和催化剂表面吸附的氮原子的再结合是氨催化分解的速率控制步骤;讨论了该催化剂体系的改进途径。     

延长氨分解器催化剂使用寿命的措施

目前,不少焦化厂的煤气净化工艺中,用催化分解炉在１０００～１２００℃下将氨分解成氮气和水,催化剂是由氧化镁作载体的负载活性镍构成的固体催化剂,氨分解炉内一般需充填８～１０ｔ催化剂,而价值高达上百万元。为此,如何延长催化剂的使用寿命,就成为降低生产成本重要环节。１影响催化剂寿命的因素氨气进入氨分解炉后,在空速一定时,氨的分解率与催化剂所含的活性镍有关,一般国产催化剂使用一年左右后,就会因活性镍减少,难以达到要求的氨分解率而更换新催化剂。催化剂失活的原因有以下两个方面：(1)镍损耗。主要是升华损耗,由…     

氨分解制氢催化剂研究进展

随着环保法规日趋严格,清洁氢能的生产和应用引起关注,氨分解制氢是其中重要途径之一。综述Ru、Ni和Fe等氨分解催化剂的研究进展,Ru催化剂具有较高的催化活性,但由于资源有限和价格昂贵等因素使其在工业应用方面受到限制。以Fe和Ni为代表的非贵金属催化剂资源丰富,价格低廉,氨分解反应转化率高,具有潜在的工业应用前景。我国独创的新一代Fe_(1-x)O基新型熔铁催化剂是目前世界上活性最高的氨合成催化剂,根据微观可逆性原理,新型熔铁催化剂也是氨分解反应活性最好的制氢催化剂。     

焦炉煤气脱氨过程中催化剂活性的检测

马格尼托哥尔斯克钢铁股份有限公司焦化厂焦炉煤气回收车间极其重视氨分解炉用催化剂活性的控制问题，并研究了在煤气净化过程中催化剂活性对整个脱氨工艺效果的影响。     

改进氨分解工艺 延长催化剂寿命

我厂的氨分解装置采用的是热催化技术，即在还原氛围下，氨和氰化氢经高温催化分解成氮、氢和一氧化碳。因氨分解炉是核心设备，仅炉内所装填催化剂的价值就高达１００万元，在保证氨分解效率的前提下，如何延长催化剂的使用寿命，则是我们日常工作的重点。１氨分解催化剂的损耗原因我们所用的氨分解催化剂是以氧化镁为载体，镍是主要活性成分。生产实践表明，在氨分解过程中造成催化剂损耗的原因有如下几方面。（１）虽然氨的分解需在高温下进行，但当温度超过１２００℃时，会使镍蒸汽压过高而加快镍的流失。当炉温低于９００℃时，则易发…     

钡离子对镍基钙钛矿分解氨的影响

镍基钙钛矿分解氨制取氢气虽有稳定性好、价格低廉的优点,但也有完全分解温度偏高的缺点。为降低完全分解氨制取氢气的温度,实验采用柠檬酸络合法,通过改变A位掺杂离子与掺杂量对LaNiO₃改性,并改变载体及负载量,制备一系列的催化剂。采用XRD、SEM、TEM表征技术进行表征,考察了Ba 含量对催化剂结构与性能的影响。实验表明在催化剂装填量为1mL、空速为10000h^-1、原料气为纯氨的条件下,氨分解的最佳电子助剂离子为Ba、最优催化剂为w(NiO)=20%的La_0.9Ba_0.1NiO₃/MCM-41,氨气完全分解温度由650℃降为575℃。随着Ba掺杂量的增加,催化剂活性先增加,在x=0.1达到最大值,之后减小,掺杂Ba过多催化剂的结构由钙钛矿变为非钙钛矿,非钙钛矿结构的催化剂活性不如钙钛矿。     

负载型氨分解催化剂的载体——高岭土的研究

为了拓展高岭土在化工领域的应用,研究了将其作为催化剂载体应用于氨分解的可行性。通过正交实验确定了高岭土载体制备过程中最大影响因素,进而确定最佳制备条件。将其制备成负载型Ni基催化剂,进行氨分解活性评价,结果表明,与工业MgO载体比较,自制高岭土载体可以达到工业MgO载体的同等水平,在氨分解反应中可替代工业MgO载体。     

载体结构对钙钛矿氨分解催化活性的影响

采用溶胶凝胶法,制备了负载型镍基钙钛矿型催化剂,并在常压微反应装置上对其氨分解催化活性进行了评价。采用BET、XRD、TPR、TEM等方法对催化剂进行表征。研究结果表明,以MCM-41分子筛为载体的催化剂,由于其较大的比表面积和规整的介孔结构,使活性组分能够很好地分散在载体表面,有利于增加有效活性位,提高活性组分的反应能力,表现出很好的氨分解催化活性。以NiO计,负载量为20%的LaNiO₃/MCM-41具有比非负载的LaNiO₃更好的催化活性,这样不仅提高了催化活性,还大大地减少了活性组分用量,降低了生产成本,从而具有很好的应用前景。     

混合法制备铁钌复合催化剂的研究

以维氏体铁催化剂为载体,以十二羰基三钌为钌的前驱体,采用固相混合法制备系列铁钌复合催化剂,考察十二羰基三钌的分解温度、热分解气氛以及钌负载量对催化剂活性的影响。采用扫描电子显微镜和热重分析等考察催化剂的表面性质与催化活性关系。结果表明,采用固相混合法得到的铁钌复合催化剂用于氨合成反应活性得到提高,在氮气气氛中,十二羰基三钌分解温度为120℃,钌负载质量分数为0.6%时,催化剂活性较好。     

Bimetallic Ru-Fe Nanoparticles Supported on Carbon Nanotubes for Ammonia Decomposition and Synthesis

Alloy catalysts can achieve superior performance to single metal while reducing the cost by fine-tuning the composition and morphology. Bimetallic Ru-Fe nanoparticles were synthesized via liquid-phase reduction method followed by impregnation with multiwall carbon nanotubes (CNTs) to prepare Ru-Fe/CNTs catalysts. The Ru₃Fe/CNTs catalyst yields a superior catalytic stability for ammonia decomposition compared to the Ru/CNTs catalyst. Hence, the ammonia synthesis rate of the Ru₃Fe/CNTs catalyst was significantly higher than that of Ru/CNTs catalyst. The potential of bimetallic catalysts with reasonable composition and proportion will expand the research of efficient catalysts for ammonia decomposition and synthesis.     

Study of the Kinetics of Ammonia Synthesis and Decomposition on Iron and Cobalt Catalysts

Activity of cobalt and iron catalysts in ammonia synthesis was determined under a pressure of 10 MPa and at the temperature range of 673–823 K, in a six-channel integral steel reactor. The catalytic ammonia decomposition was studied in a differential reactor under the atmosphere of low concentration of ammonia (<6%) in the temperature range of 673–823 K under atmospheric pressure. The determined values of the activation energy for the ammonia synthesis reaction over cobalt and iron catalysts are 268 and 180 kJ/mol, respectively, whilst for the ammonia decomposition reaction they are equal to 111 and 138 kJ/mol. The cobalt catalyst showed lower activity than a commercial iron catalyst in ammonia synthesis reaction. The cobalt catalyst turned out to be more effective in ammonia decomposition reaction than the iron one.     

Catalytic ammonia decomposition: COx-free hydrogen production for fuel cell applications

Catalytic decomposition of ammonia has been investigated as a method to produce hydrogen for fuel cell applications. The absence of any undesirable by-products (unlike, e.g., CO_x, formed during reforming of hydrocarbons and alcohols) makes this process an ideal source of hydrogen for fuel cells. In this study a variety of supported metal catalysts have been studied. Supported Ru catalysts were found to be the most active, whereas supported Ni catalysts were the least active. The supports were found to play a profound role in the ammonia decomposition process. The activation energies for the ammonia decomposition process varied from 17 to 22 kcal/mol depending upon the catalyst employed. The activation energies of the supported Ir catalysts were found to be in excellent agreement with our recent studies addressing ammonia decomposition on single crystal Ir.     

镍基氨分解制氢催化剂的制备及性能

用浸渍法制备Ni/Al_2O_3和Ni/xMo-Al_2O_3催化剂,以氨分解为模型反应,考察Ni负载量、焙烧温度、溶剂和助剂等合成条件对催化剂催化性能的影响,通过XRD和TG-DTG表征方法对催化剂进行表征。结果表明,最佳合成条件:Ni负载质量分数为16%,焙烧温度350℃,采用丙酮为溶剂制备的Ni/Al_2O_3催化剂具有较好的催化活性。500℃添加质量分数3%的助剂Mo可以使Ni/Al_2O_3催化剂的活性显著提高39%,Ni/3%Mo-Al_2O_3催化剂的氨分解率达93.5%。     

Preparation of propylene carbonate by alcoholysis of urea from the perspective of homogeneous reaction: Influence of dissolution and precipitation of metal oxide catalysts

The dissolution process of metal oxide catalysts in the alcoholysis of urea by 1, 2-propylene glycol (PG) to the synthesis of propylene carbonate (PC) was investigated. It was found that the reaction was mainly catalyzed by homogeneous catalysts. The metal oxide reacted with ammonia and isocyanate acid, the decomposition products of urea, to form a complex and dissolved into the reaction system. The dissolved amount of catalyst was positively correlated with the PC yield by using different oxides and salts as catalysts. The Fourier-transform infrared spectroscopy (FTIR) result of the catalysts reacting with urea showed that the dissolution-precipitation process of the catalysts was related to the decomposition of urea. The results of catalytic test indicated that both the dissolved amount of catalysts and the structure of the complex affected PC yields. A reaction mechanism was proposed based on the results. From the mechanism, a complex catalyst with at least two ammonia ligands is better for this reaction.     

耐高温焦炉煤气氨分解催化剂的研究

研究了经过改进的MgO载体对NH3分解活性和反应热稳定性的影响。在容易造成催化剂烧结的高温、水蒸气等条件下,对催化剂进行活性评价;通过超高温处理,观察催化剂活性下降情况,配合XRD分析结果以及SEM照片,发现通过ZrO2修饰载体和特定方法制备的催化剂,在高温下能够较好地抑制Ni、Co活性组分的烧结,具有良好的热稳定性。