氨制冷技术的应用现状及发展趋势

剖析氨制冷剂的特点,分析国内外氨制冷系统的应用现状和存在的问题;从氨制冷系统优化、控制技术提高、安全性保障、氨系统小型化以及我国在氨制冷系统设计规范、设计手册中对安全性的要求等多个方面阐述氨制冷技术的发展趋势和尚需逐步解决的问题;提出简化氨制冷系统的具体思路;指出我国应加速研发小型氨制冷压缩机,重视氨制冷设备及应用的理论与试验研究,以简化系统、推进小型化进程,拓展氨制冷系统的应用领域。     

A comparative study of hydrothermal aging effect on cerium and lanthanum doped Cu/SSZ-13 catalysts for NH_3-SCR

Ce-or La-doped Cu/SSZ-13 catalysts were prepared by a hydrothermal method and Cu,Ce or La ions were incorporated through stepwise ion exchange,The catalyst activity was measured for the ammonia selective catalytic reduction reaction.The structure and composition of catalyst were characterized by using X-ray diffraction,scanning electron microscopy,inductively coupled plasma mass spectrometry solid-state NMR,NH_3-TPD techniques,and the active components were examined by XPS and XANES.The results indicate that the Ce and La doping can both completely preserve the SCR activity of Cu/SSZ-13 above 300℃,but there is also a decrease of activity below 200℃.On the other hand,Ce doping is beneficial to the formation of framework aluminum,stabilizes molecular sieve framework and Cu active sites of Cu/SSZ-13,thereby improves the catalyst hydrothermal stability.But La doping will decrease the amount of framework aluminum and Cu active sites of Cu/SSZ-13 after hydrothermally aging,even destroy zeolite CHA structure.This is quite harmful to the catalyst hydrothermal stability.     

Ni0.09Ti0.91O2纳米颗粒和纳米管负载铜的催化脱硝性能和机理

随着氮氧化物危害的日益加剧,脱硝催化剂的发展已成为对其进行治理的关键因素。本文通过水热、煅烧两步法制备了Ni0.09Ti0.91O2纳米管负载铜的脱硝催化剂,研究了该类催化剂的结构和脱硝性能。采用N2物理吸附、X射线衍射、扫描电子电镜、透射电镜等方法确定了催化剂的结构,Ni0.09Ti0.91O2纳米管为锐钛矿结构,铜原子团簇分布在纳米管表面,氮气吸脱附实验测定Ni0.09Ti0.91O2负载铜前后的比表面积分别为263.51和216.5422 m2 g-1,纳米管表面铜分散均匀,提高了其催化脱硝性能,Ni0.09Ti0.91O2纳米管负载7 wt%铜催化剂的脱硝效率接近100%,而且具有良好的抗中毒性能。原位漫反射红外光谱测试表明其 NH3-SCR 过程遵循L-H机制,作为对比文章同时研究了Ni0.09Ti0.91O2纳米颗粒负载铜的脱硝性能。Ni0.09Ti0.91O2纳米管负载7 wt%铜催化剂显示出良好的应用前景。     

超支化聚酯改性超细氧化锌

采用富含—COOH基团的超支化聚酯(HBP)对超细氧化锌(μ-ZnO)进行表面改性,并对改性后的氧化锌的结构和特征进行了表征。结果表明：在氨水中得到了稳定期较长、清澈透明的μ-ZnO悬浮液,在n(—COOH)／n(μ-ZnO)为1／8时稳定期最长,超过72h;采用相同的方法,但溶剂为丙酮或乙酸丁酯时,稳定期只有0．5～1h;改性后的μ-ZnO在1575cm^-l处出现新的振动吸收,表面包覆了聚合物,团聚现象不明显,分散状态得到明显的改善。     

Potential of green ammonia production in India

The threat of climate change is forcing the world to decarbonize all economic sectors. Ammonia primarily used for fertilizer production and a potential, ‘hydrogen carrier’ currently accounts for ~27% of global hydrogen consumption and ~1% of global greenhouse gas emissions. In this analysis, we assess the techno-economic potential of ammonia production using onshore wind, open-field photovoltaic and batteries for both domestic usage and export scenarios in India, which is currently one of the world's largest producer and importer of ammonia. Our results reveal that India's potential can comfortably satisfy global ammonia demand with lowest ammonia costs of 723 EUR/t_NH3 and 765 EUR/t_NH3 for the domestic and export scenario, respectively. To compete with conventional ammonia production a carbon tax of 224–335 €/t_CO2 would be required. Finally, costs of shipping liquid hydrogen and the ‘hydrogen carrier’ ammonia are similar here giving other economic, environmental and safety factors higher relevance.     

Hydrogen production from ammonia decomposition using Co/γ-Al2O3 catalysts – Insights into the effect of synthetic method

Chemical hydrogen storage in molecules such as ammonia (>17 wt% H₂) have the unique potential to overcome the current storage and transport limitations of the H₂ economy. However, sustainable on-demand production of hydrogen via ammonia decomposition, requires the development of novel transition metal-based catalysts beyond the current use of highly active but expensive ruthenium to ensure economic feasibility. In this paper, we provide fundamental understanding of the effects of a range of synthetic methods of Co/γ-Al₂O₃ catalysts on the resulting ammonia decomposition activity. The main activity determining factors are collectively the reducibility of the cobalt species and their particle size. This systematic work demonstrates that decreasing the cobalt particle size enhances the ammonia decomposition catalytic activity. However, a careful balance is required between a strong metal-support interaction leading to small particle sizes (promoted by precipitation methods) and the formation of inactive cobalt aluminate species (encouraged by adsorption methods). In addition, impurities such as boron and chloride remaining from particular synthetic methods were found to have detrimental effects on the activity.     

Metal-free rapid dehydrogenation kinetics and better regeneration yield of ammonia borane

Ammonia borane (AB), one of the promising hydrogen storage materials, is receiving more attention because of its high hydrogen content. However, to act as a sustainable material for hydrogen storage, regeneration from products obtained on dehydrogenation is essential. Regeneration of AB reported in literature involves the use of expensive reagents with high toxicity and environmental impact. In this work, we attempted to aid the dehydrogenation/regeneration process of pure ammonia borane as well as products obtained on thermolysis of AB, using acetone as the dehydrogenation/digestion reagent. During dehydrogenation, a total of 1.7 equivalent of hydrogen was obtained through a thermal and chemical reaction with the resultant formation of tri and tetrasubstituted borate ester. In the current work, a simple method for regeneration of AB is being demonstrated from the dehydrogenated products, which are borate esters, in this case. Using this method, an overall regeneration yield, i.e., from starting material AB→ dehydrogenated products→ regenerated material AB is observed to be 68%. The conversion yield of regenerated AB, starting from dehydrogenated products, was found to be 83%, and that into hydrazine borane (HzB) to be 15% (which can also act as hydrogen source).     

Study on the mechanism of the ignition process of ammonia/hydrogen mixture under high-pressure direct-injection engine conditions

As environmental problems and energy crisis become more serious, ammonia is one of the potential alternative fuels. In order to better use ammonia as fuel in power equipment, the ignition process was studied under high-pressure direct-injection engine condition. In the paper, the Homogeneous model in Chemkin package was selected for numerical calculation. In the six cases with different hydrogen mixing ratios, the effect of initial temperature, pressure, equivalence ratio and hydrogen mixing ratio on ignition delay time (IDT) were studied. It conducted that IDT could be effectively reduced when adding 10–50% hydrogen to ammonia. Then, after sensitivity analysis of NH₃/H₂ mixtures, the key equations and free radicals affecting combustion characteristics were found. The rate of production (ROP) of the key radicals were carried out. It was found that the hydrogen provided the initial concentration of H radical before the start fire, which greatly improved the ROP of OH radical of R1(H + O₂=O + OH) compared to the original H needed to break the N–H chemical bond in pure ammonia. And the OH radical was related to the consumption of NH₃ by R31(NH₃+OH=NH₂+H₂O).