Carbon dioxide hydrogenation: Efficient catalysis by an NHC-amidate Pd(II) complex

The utilization of carbon dioxide as a carbon source has long been a challenge in modern organic chemistry due to its low reactivity, yet high abundance. Herein we demonstrate the highly efficient hydrogenation of carbon dioxide into formic acid in the presence of an NHC-amidate Pd(II) complex. Excellent turnover number was observed when the catalyst was used under heterolytic conditions. This catalytic system provides a new and efficient carbon dioxide hydrogenation method.     

功能化MCM-41固载的钌基催化剂上二氧化碳加氢合成甲酸

采用两种方法制备了功能化MCM-41固载的钌基催化剂,并用原子吸收光谱,紫外可见光谱以及红外光谱等手段对其进行表征。结果表明,钌基在功能化MCM-41上顺利固载。将这两种固载的钌基催化剂用于二氧化碳加氢合成甲酸反应,发现在较低反应温度和较低氢分压下,固载的RuCl2(PPh3)3催化剂表现出更高的催化活性,在反应温度80℃,H2分压5MPa, CO2分压8MPa下,甲酸转化数达到1275。固载的RuCl2(PPh3)3催化剂也表现出很好的重复再用性。     

Temperature-dependent growth shapes of Ni nanoclusters on NiAl(110)

Scanning tunneling microscopy studies reveal that two-dimensional nanoscale Ni islands formed by deposition of Ni on NiAl(110) between 200-400 K exhibit far-from-equilibrium growth shapes which change systematically with temperature. Island structure reflects the two types of adsorption sites available for Ni adatoms, and island shapes are controlled by the details of adatom diffusion along island edges accounting for numerous local configurations. The temperature dependence of the island shapes is captured and elucidated by kinetic Monte Carlo simulation of a realistic atomistic-level multisite lattice-gas model incorporating precise diffusion barriers. These barriers are obtained by utilizing density functional theory to probe energetics not just at adsorption sites but also at transition states for diffusion. This success demonstrates a capability for predictive atomistic-level modeling of nanocluster formation and shape selection in systems that have a high level of energetic and kinetic complexity.     

Carbon dioxide hydrogenation to formic acid by using a heterogeneous gold catalyst

AUROlite, consisting of gold supported on titania (picture shows extrudates in a steel net cage), is a robust catalyst for the production of catalyst-free HCOOH/NEt(3) adducts from H(2), CO(2), and neat NEt(3). Pure HCOOH is freed from the adducts by amine exchange.     

氢原子在Ni(100), Ni(111)和Ni(110)面上吸附扩散势能面的结构

本文构造了氢-镍相互作用的5参数Morse势, 用经典的对势方法研究氢原子在Ni(100), Ni(111)和Ni(110)面上的吸附和扩散, 得到氢原子在三个表面上的吸附位、吸附几何、结合能及本征振动等数据, 和实验结果符合得很好。同时, 系统地研究了三个体系的吸附扩散势能面结构。     

Tilted CO on metal surfaces; CO/Pt(110), CO/Ni(110) and CO/Cu(100)

Tilting of CO at coverages greater than half a monolayer is considered as a mechanism for reducing the CO-CO repulsion. We find qualitative agreement with the experiment for CO/Pt(110), and predict a slightly smaller tilt for CO/Ni(110). For CO/Cu(100), we find that a bend of about 10° greatly reduces the repulsion.     

Ab initio calculations for adsorbed state of OH group on Ni(110)

Ab initio quantum-chemical calculations of OH radical adsorption on Ni(110) have been carried out in cluster approximations. It is shown that unlike energy calculations of adsorbed complexes, their vibrational frequencies must be calculated with taking into account 3d orbitals of Ni.

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OH Ni(110) . , , 3d-.

     

甲醛在Ni(110)面上分解的分子轨道研究

本文应用CNDO方法研究了H_2CO在Ni(110)面上的分解反应。证明了金属镍使H_2CO对称禁阻的热分解反应变成了对称允许反应; 讨论了H_2CO在Ni(110)面上的各种吸附模型; 论证了卧式多中心吸附作为H_2CO分解的中间步骤。     

Carbon dioxide adsorption by physisorption and chemisorption interactions in piperazine-grafted Ni(2)(dobdc) (dobdc = 1,4-dioxido-2,5-benzenedicarboxylate)

The metal-organic framework Ni(2)(dobdc) (CPO-27-Ni, where dobdc = 1,4-dioxido-2,5-benzenedicarboxylate) has been post-synthetically modified with piperazine (pip) - a known 'accelerator' to improve the kinetics of CO(2) uptake in alkanolamine solvents for chemical absorption - and the impact of the modification on the CO(2) uptake and selectivity over N(2) has been probed. While the modified framework, Ni(2)(dobdc)(pip)(0.5) (pip-CPO-27-Ni), exhibits a lower uptake of CO(2) compared with the non-grafted material, the selectivity for CO(2) over N(2) at 25 °C and at pressures pertinent to post-combustion flue gas capture (0.1-0.15 bar) is enhanced. Mechanistically, the interaction between the CO(2) molecules and the free amine sites in pip-CPO-27-Ni occurs via physisorption and chemisorption interactions, in which CO(2) binds to the framework with an isosteric heat of adsorption (-Q(st)) of 40.5 kJ mol(-1) at very low coverage (P = 0.033 mbar), followed by binding at a higher heat of adsorption (-Q(st) = 46.2 kJ mol(-1) at P = 3.55 mbar). Pure water adsorption isotherms revealed a two-step mechanism for uptake in CPO-27-Ni, consistent with adsorption into the first and second hydration spheres of Ni(2+) followed by subsequent uptake via physisorption into the pores. Additional steric hindrance in pip-CPO-27-Ni results in a single step only. The working capacity over multiple cycles was also investigated using a temperature swing adsorption process which revealed reversible CO(2) adsorption and desorption of 10 wt% over 10 cycles.     

HCOO在Cu(110)、Ag(110)和Au(110)表面的吸附

采用密度泛函理论(DFT)以及广义梯度近似方法(GGA)计算了甲酸根(HCOO)在Cu(110)、Ag(110)和Au(110)表面的吸附. 计算结果表明, 短桥位是最稳定的吸附位置, 计算的几何参数与以前的实验和计算结果吻合. 吸附热顺序为Cu(110)(-116 kJ·mol-1)>Ag(110)(-57 kJ·mol-1)>Au(110)(-27 kJ·mol-1), 与实验上甲酸根的分解温度相一致. 电子态密度分析表明, 吸附热顺序可以用吸附分子与金属d-带之间的Pauli 排斥来关联, 即排斥作用越大, 吸附越弱. 另外还从计算的吸附热数据以及实验上HCOO的分解温度估算了反应CO2+1/2H2→HCOO的活化能, 其大小顺序为Au(110)>Ag(110)>Cu(110).     

RAIRS at higher pressures: Ni(110)-CO and Cu(111)-CO

A cell is described for reflection-absorption i.r. spectroscopy (RAIRS) of species on metal single crystal surfaces at pressures up to 1 atm. in conjunction with UHV surface characterization facilities. Concurrent wavelength modulation and beam chopping provide spectra recorded alternately in p and s polarization for effective discrimination between surface and gas-phase bands. Spectra of CO adsorbed on Ni(110) and Cu(111) illustrate the application of this method to a reacting system and problems of surface contamination at high pressures.     

硫在Ni_(110)表面偏析的角分辨俄歇研究

本实验采用LEED及角分辨俄歇两种手段,对硫在Ni_(110)表面的偏拆作了详细的分拆。角分辨俄歇表明:Ni_(110)表面硫的偏折存在一硫的深度分布,分布层厚度大约为2～3镍原子层厚度。而LEED观察表明,当退火温度达到900℃退火4～5秒,将得到清晰的C_(2×2)图形。     

A Density Functional Study of Ozone and Oxygen Surface Structures on Ni(110)

The dissociative and molecular forms of O₃ adsorbed on nickel were studied by the density functional method (Becke3LYP exchange correlation functional). The energy profile of the ozone decomposition reaction (O₃)_gas (O₃)_ads (O₂)_ads+1/2O₂ on the Ni₁₀ surface cluster was calculated. As opposed to the weakly bound molecular form of oxygen on transition metals, ozone forms a tightly bound surface compound on the surface of nickel. It is attempted to evaluate the heat of oxygen adsorption on the defective surface of Ni using the model of the surface cluster Ni₁₃ with a vacancy . The positions of the surface nickel atoms before and after their interaction with the adsorbate were calculated. It is shown that substantial relaxation of the surface nickel atoms takes place in the course of adsorption. The possibility of stabilization of the molecular ozone-like form of oxygen on the surface of transition metals in conditions of high oxygen coating extent is discussed.     

Structure and properties of Ni(110) surface coadsorbing chlorine and oxygen

The coadsorption of chlorine with oxygen on Ni(110) surface has been investigated by XPS, UPS, AES and work function measurements. The chlorine preadsorption drastically inhibits the further uptake of oxygen. On the contrary, precovered oxygen has hardly any influence on the additional adsorption of chlorine due to the incorporation of precovered oxygen into the subsurface driven by the chlorine coadsorption. ARXPS measurements provide the evidence for this coadsorption model. The thermal desorption of chlorine and oxygen from the coadsorption surface is very similar to that of both individual adsorbates under the same heating conditions, but the desorption temperature of both the adsorbates apparently decreases on the coadsorption surface. The coadsorption and thermodesorption mechanisms are also discussed in detail.     

The chemisorption of carbon monoxide on Ni(110) studied by electron energy loss spectroscopy

The vibrational spectrum of carbon monoxide chemisorbed on Ni(110) at 300K has been recorded as a function of surface coverage. At low and intermediate coverage the adsorbate is bonded either to single nickel atoms (linear site) or to two nickel atoms in contact (B₂ site). As the coverage approaches unity the spectrum changes rapidly until at saturation virtually all adsorbed molecules are of B₂ type.     

Ni(111)表面上N原子对C原子电子结构的影响

N是金刚石中的主要杂质之一, 为了研究金刚石生长过程中杂质N对C电子结构转化的影响, 用密度泛函理论研究了Ni(111)表面上C与N共吸附的三个不等价模型, 同时建立了三个C吸附模型作为比较. 计算结果表明, N原子的出现使得吸附体系相对不稳定, 吸附原子之间的相互作用不能忽略; 通过比较相互作用能可以看出, 相同的吸附位下C-C相互作用比C-N 相互作用强. 通过比较不同模型中C原子分波态密度可以看出, N-C相互作用一定程度上增加了Ni的催化活性, 但是与C-C自身的相互作用比较起来效果并不明显. 吸附几何结构和分波态密度还表明, 当吸附的原子过于紧密以致占有同一个Ni(111)-(1×1)晶胞表面时, 就会形成CN化合物或者类石墨杂质.     

Structural and kinetic effects on a simple catalytic reaction: oxygen reduction on Ni(110)

Oxygen hydrogenation at 100 K by gas phase atomic hydrogen on Ni(110) has been studied under ultrahigh vacuum conditions by temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). Formation of adsorbed water and hydroxyl species was observed and characterized. The coverage of the reaction products was monitored as a function of both temperature and initial oxygen precoverage. On the contrary, when high coverage oxygen overlayers were exposed to gas phase molecular hydrogen, no hydrogenation reaction took place. The results are compared to the inverse process, exposing the hydrogen covered surface to molecular oxygen. In this case, at 100 K, simple Langmuir-Hinshelwood modeling yields an initial sticking coefficient for oxygen adsorption equal to 0.26, considerably lower than for the clean surface. Moreover, formation of hydroxyl groups is found to be twice as fast as the final hydrogenation of OH groups to water. Assuming a preexponential factor of 10(13) s(-1), an activation barrier of 6.7 kcal/mol is obtained for OH formation, thus confirming the high hydrogenating activity of nickel with respect to other transition metals, for which higher activation energies are reported. However, oxygen is hardly removed by hydrogen on nickel: this is explained on the basis of the strong Ni-O chemical bond. The hydrogen residual coverage is well described including a contribution from the adsorption-induced H desorption process which takes place during the oxygen uptake and which is clearly visible from the TPD data.     

The mechanism of methanol formation and other reactions following formaldehyde adsorption on Ni(110)

The adsorption/desorption and reactive behavior of formaldehyde was studied on clean single-crystal Ni(110) at adsorption temperatures down to 200 °K. For low exposures of the surface to formaldehyde, hydrogen and CO binding states were populated due to decomposition of the molecule upon adsorption. Higher exposures gave rise to a decomposition-limited hydrogen peak exhibiting an activation energy of 20 kcal/gmol and an apparent frequency factor of 10¹⁴ sec^?1. At initial coverages of H₂CO exceeding about 0.5, monolayer methanol was observed to form. The formation of methanol involved a hydrogen atom transfer between two adsorbed H₂CO molecules and did not occur totally via surface hydrogen. Self-oxidation to form CO₂ was also observed. The surface exhibited reaction heterogeneity, and the surface reactivity was observed to depend on the temperature of adsorption of reactants, suggesting strong adsorbate-induced surface “reconstruction.”     

Carbon dioxide reforming of methane on monolithic Ni/Al2O3-based catalysts

Nickel-alumina catalysts supported on cordierite monoliths of honeycomb structure surpass essentially the conventional granulated ones with respect to the output in carbon dioxide reforming of methane. Adjusting the surface acid-base properties of catalysts by introduction of alkali metal (Na, K) oxides inhibits the carbonization and as a result, improves the operational stability of these catalysts. An effect of promotion of nickel-alumina based composite doped by lanthanum oxide is found. This effect, caused by an additional route for the CO2 activation on Ni-La2O3/Al2O3/cordierite catalyst, is displayed in increase of methane conversion under conditions of an oxidant excess.     

Carbon dioxide hydrogenation catalyzed by a ruthenium dihydride: a DFT and high-pressure spectroscopic investigation

Reaction pathways during CO(2) hydrogenation catalyzed by the Ru dihydride complex [Ru(dmpe)(2)H(2)] (dmpe=Me(2)PCH(2)CH(2)PMe(2)) have been studied by DFT calculations and by IR and NMR spectroscopy up to 120 bar in toluene at 300 K. CO(2) and formic acid readily inserted into or reacted with the complex to form formates. Two formate complexes, cis-[Ru(dmpe)(2)(OCHO)(2)] and trans-[Ru(dmpe)(2)H(OCHO)], were formed at low CO(2) pressure (<5 bar). The latter occurred exclusively when formic acid reacted with the complex. A RuHHOCHO dihydrogen-bonded complex of the trans form was identified at H(2) partial pressure higher than about 50 bar. The trans form of the complex is suggested to play a pivotal role in the reaction pathway. Potential-energy profiles along possible reaction paths have been investigated by static DFT calculations, and lower activation-energy profiles via the trans route were confirmed. The H(2) insertion has been identified as the rate-limiting step of the overall reaction. The high energy of the transition state for H(2) insertion is attributed to the elongated Ru--O bond. The H(2) insertion and the subsequent formation of formic acid proceed via Ru(eta(2)-H(2))-like complexes, in which apparently formate ion and Ru(+) or Ru(eta(2)-H(2))(+) interact. The bond properties of involved Ru complexes were characterized by natural bond orbital analysis, and the highly ionic characters of various complexes and transition states are shown. The stability of the formate ion near the Ru center likely plays a decisive role for catalytic activity. Removal of formic acid from the dihydrogen-bonded complex (RuHHOCHO) seems to be crucial for catalytic efficiency, since formic acid can easily react with the complex to regenerate the original formate complex. Important aspects for the design of highly active catalytic systems are discussed.