有富电子镍位点的耐酸金属间化合物CaNi_(2)Si_(2)催化剂用于不饱和有机酸酐/酸的水相加氢

顺酐水相加氢制备下游产物丁二酸,是一种合成生物可降解塑料聚丁二酸丁二醇酯的重要单体.在水相体系中,顺酐迅速水解生成顺丁烯二酸,表现出较强的酸性,对催化剂耐酸稳定性要求较高.贵金属催化剂通常表现出较高的顺酐加氢活性,但由于其与底物分子结合能力较强,容易生成深度加氢或氢解产物,并且贵金属高昂的价格也限制了其进一步应用.此外,工业上常用的负载型Ni基催化剂的活性和稳定性也有待进一步提高.因此,在顺酐水相直接加氢生成丁二酸的过程中开发高活性和高稳定性的非贵金属基催化剂具有重要意义.金属硅化物作为一种新型的金属间化合物催化材料,常作为非均相催化剂应用,尤其对涉氢反应表现出较高的活性和选择性,并且由于硅原子的掺入,调变了活性位点的几何和电子结构,使其展现出较好的催化活性、耐酸碱腐蚀性和热稳定性,有望用于顺酐直接水相加氢反应制备丁二酸.本文采用新型低温熔盐技术成功制备了一种单相的、元素分散均匀以及高比表的CaNi_(2)Si_(2)金属间化合物纳米催化剂,并将其应用于顺酐连续水相加氢制备丁二酸的反应体系中,可以有效解决该体系存在的瓶颈问题.采用X射线衍射Rietveld精修技术、X射线光电子能谱深度剖析、紫外光电子能谱和态密度分析等手段对CaNi_(2)Si_(2)催化剂的几何和电子结构进行剖析.并采用模型化合物丙烯酸原位漫反射傅里叶变换红外光谱、原位程序升温脱附/表面反应及密度泛函理论计算等研究了CaNi_(2)Si_(2)催化顺酐加氢反应机理,并剖析构效关系.结果表明CaNi_(2)Si_(2)催化剂中电子由Ca向Ni和Si发生转移,并证明了这种富电子Ni活性位点的协同作用有利于其对底物分子中C=C键选择性吸附和H_(2)的活化,从而使其展现出较好的目标产物丁二酸的选择性.在3 MPa,120℃,接触时间5.4 gcat/(mmolreactant·min^(‒1))条件下,丁二酸产率可达到100%.此外,相比于负载型Ni/SBA-15催化剂(51.90 kJ/mol),CaNi_(2)Si_(2)展现出更低的表观活化能(46.39 kJ/mol),从本征活性证明了其作为顺酐水相加氢催化剂的优势.稳定性测试结果表明,与Ni/SBA-15相比,由于CaNi_(2)Si_(2)中Ni特殊的配位环境和电子结构抑制了羧酸盐的形成,有效减少了活性金属Ni位点的流失,从而有效的提高了其在顺酐水溶液(2 wt%,pH=1.51)中的耐酸腐蚀性能,使其表现出高活性的同时具有较好稳定性,在一定程度上可替代贵金属催化剂.同时,底物扩展实验也证明了CaNi_(2)Si_(2)作为一种催化新材料在不饱和链状或环状有机酸/酸酐的加氢性能反应中均能展现出较好的活性,说明了CaNi_(2)Si_(2)作为非贵金属催化剂在酸酐加氢领域具有巨大潜力.总之,金属硅化物的精细设计和结构调控将为顺酐加氢催化剂的可控优化提供重要参考,并为设计高效稳定的苛刻反应中选择性加氢催化剂提供新的思路.

Boosting the Performance Gain of Ru/C for Hydrogen Evolution Reaction Via Surface Engineering

The surface properties of catalysts determine the intrinsic activity and adaptability.Ruthenium is regarded as a potential candidate to substitute platinum for water electrolysis due to the low cost and analogous electronic structures while it suffers from severe dissolution and stability problems.Herein,the modification of Ru/C with atomically dispersed cobalt atoms is achieved via a simple thermal doping method.The newly formed amorphous shell with Ru-Co sites on the Ru/C catalyst improved the hydrogen evolution reaction activity and stability significantly.Impressively,the obtained Co1Ru@Ru/CN_(x)catalyst exhibited an overpotential as low as 30 mV at 10 mA cm^(-2)in an alkaline medium,which is among the best HER catalysts reported so far.The oxygen oxophile Co prevents the fast oxidation and dissolution of Ru species,ensuring outstanding long-term durability up to 70 h.Theoretical calculations reveal that the Ru-Co coordination acts as a more active site for water dissociation than the Ru-Ru.Meanwhile,the"Ru-Co shell/Ru core"structures show high adaptability for the reaction conditions.This simple doping strategy offers prospects for scalable preparation of highly active electrocatalysts.

Three-Dimensional Simulation of Hydrodynamic Mechanism of Fluidized Bed Methanation

Organic solid waste(OSW)contains many renewable materials.The pyrolysis and gasification of OSW can realize resource utilization,and its products can be used for methanation reaction to produce synthetic natural gas in the specific reactor.In order to understand the dynamic characteristics of the reactor,a three-dimensional numerical model has been established by the method of Computational Fluid Dynamics(CFD).Along the height of the reactor,the particle distribution in the bed becomes thinner and the mean solid volume fraction decreases from 4.18%to 0.37%.Meanwhile,the pressure fluctuation range decreased from 398.76 Pa at the entrance to a much lower value of 74.47 Pa at the exit.In this simulation,three parameters of gas inlet velocity,operating temperature and solid particle diameter are changed to explore their influences on gas-solid multiphase flow.The results show that gas velocity has a great influence on particle distribution.When the gas inlet velocity decreases from 6.51 to 1.98 m/s,the minimum height that particles can reach decreases from 169 to 100 mm.Additionally,as the operating temperature increases,the particle holdup inside the reactor changes from 0.843%to 0.700%.This indicates that the particle residence time reduces,which is not conducive to the follow-up reaction.Moreover,with the increase of particle size,the fluctuation range of the pressure at the bottom of the reactor increases,and its standard deviation increases from 55.34 to 1266.37 Pa.

Study of the role of alkaline sodium additive in selective hydrogenation of phenol

The selective hydrogenation of phenol to cyclohexanone is an important process in the chemical industry.However,achieving high selectivity at high conversion rates is highly challenging,particularly under continuous reaction conditions.Here,we found that the presence of Na alkaline additives(NaX,X=CO3^2–,HCO^3–,or OH^–)on Pd/Al2O3 not only promoted the phenol conversion from 8.3%to>99%but also increased the cyclohexanone selectivity from 89%to>97%during the continuous hydrogenation of phenol on a fixed bed reactor.After 1200 h of continuous reaction,no activity or selectivity attenuation was observed and the turnover number was approximately 2.9×10^5.Density functional theory calculations,spectroscopic,and dynamics studies demonstrated that the addition of NaX greatly promoted phenol adsorption and hydrogen activation,thereby improving catalytic activity.Simultaneously,the formation of a“-C=O-Na-”intermediate inhibited the excessive hydrogenation and intermolecular coupling of cyclohexanone,leading to high selectivity.

Highly performed platinum nanosheets synthesized under in situ reaction conditions for hydrogen generation

Surface properties of a catalyst, especially exposed crystal facets and coordination states, directly affect the catalyst's performance. Herein, we illustrate how reaction conditions direct the fabrication of a wellbehaved catalyst with desired structures in the case of hydrogen evolution reaction(HER). Stable adsorbed PtClxions on CNTs are in situ electrochemically reduced into a unique Pt nanosheet structure enclosed by high-index(311) and low-index(200) and(111) facets during HER process. Experimental results and density functional theory(DFT) calculation disclose the function mechanism between these unique structures and reactants. The adsorbed H2 O and reactive species act as capping agents protecting the(311) facet where the dissociation of water molecule is promoted, and the produced H*intermediates favorably combine and release on the nearby low-index Pt sites. The joint collaborations of these active sites afford Pt nanosheets comparable activity to 20 wt% Pt/C and a 12.7-fold over mass activity. These findings provide novel insight into the synthesis of heterogeneous catalysts with high specificity.

Insight into rare-earth-incorporated catalysts:The chance for a more efficient ammonia synthesis

Recent studies have suggested that rare earth(RE)elements in catalysts significantly influence the performance of the ammonia synthesis.The REs appear in various forms in the ammonia synthesis catalysts including supports(oxides,hydrides,and nitrides),promotors,and intermetallic.Besides the conventional RE oxide-supporting catalysts(mainly Ru/REO),some new RE-containing catalyst systems,such as electrode and nitride systems,could drive the ammonia synthesis via a benign Mars-van Krevelen mechanism or multi-active-site mode,affording high ammonia synthesis performance under mild conditions.These works demonstrate the great potential of RE-containing catalysts for more efficient ammonia synthesis.This review summarizes the contributions of different kinds of RE-based catalysts and highlights the function mechanism of incorporated REs.Finally,an overview of this area and the challenges for further investigation are provided.

Crystal and electronic structure engineering of tin monoxide by external pressure

Although tin monoxide (SnO) is an interesting compound due to its p-type conductivity,a widespread application of SnO has been limited by its narrow band gap of 0.7 eV.In this work,we theoretically investigate the structural and electronic properties of several SnO phases under high pressures through employing van der Waals (vdW) functionals.Our calculations reveal that a metastable SnO (β-SnO),which possesses space group P2_(1)/c and a wide band gap of 1.9 eV,is more stable than α-SnO at pressures higher than 80 GPa.Moreover,a stable (space group P2/c) and a metastable (space group Pnma) phases of SnO appear at pressures higher than 120 GPa.Energy and topological analyses show that P2/c-SnO has a high possibility to directly transform to β-SnO at around 120 GPa.Our work also reveals that β-SnO is a necessary intermediate state between high-pressure phase Pnma-SnO and low-pressure phase α-SnO for the phase transition path Pnma-SnO →β-SnO →α-SnO.Two phase transition analyses indicate that there is a high possibility to synthesize β-SnO under high-pressure conditions and have it remain stable under normal pressure.Finally,our study reveals that the conductive property of β-SnO can be engineered in a low-pressure range (0-9 GPa)through a semiconductor-to-metal transition,while maintaining transparency in the visible light range.