Effective and selective direct aminoformylation of nitroarenes utilizing palladium nanoparticles assisted by fibrous-structured silica nanospheres

Research on Chemical Intermediates - Palladium nanoparticles (~?1–3 nm, 0.4 wt% Pd) were uniformly distributed over the surface of fibrous silica nanospheres (KCC-1)...     

金掺杂对碳负载钯催化还原性能的促进作用

在许多催化应用中双金属的PdAu催化剂性能优于单金属催化剂.科研人员对具有可控纳米结构和高活性的PdAu催化剂进行了广泛的研究,但该催化剂的制备需要多步且通常步骤复杂.本文仅通过浸渍和焙烧制得了Au掺杂的负载型Pd催化剂,所得PdAu/C催化剂用于室温水相三氯乙烯加氢脱氯反应.当Pd和Au负载量分别为1.0 wt%和1.1 wt%时,在经过干燥、空气处理和H2还原的过程后，所制得的PdAu/C催化剂活性最高,初始转化频率(TOF)为34.0×10–2 molTCEmolPd–1 s–1,是单金属1.0 wt%Pd/C催化剂TOF (2.2×10–2 molTCEmolPd–1 s–1)的15倍以上. X射线吸收光谱结果表明,金的加入避免了400oC焙烧时Pd的氧化.本文还提出了可能的催化剂纳米结构演变路径,以解释所观察到的催化现象.     

Influence of CeO2 and La2O3 on properties of palladium catalysts used for emission control of natural gas vehicles

Pd/YZ-Al2O3 (Y and Zr modified Al2O3, and hereafter, labelled as Al) catalysts with 4 wt% additive CeO2 and/or La2O3 were prepared and characterized by X-ray photoelectron spectroscopy (XPS), NO-temperature programmed desorption (NO-TPD), N2-adsorption/desorption (Brunauer-Emmet-Teller BET method), X-ray diffraction (XRD) and CO-chemisorption. Catalytic activities for CH4, CO and NO conversion were tested in a gas mixture simulated the emissions from natural gas vehicles (NGVs) operated under stoichiometric conditions. The results indicated that all catalysts exhibited excellent catalytic performances for CH4 and CO oxidation and the promoting effect of CeO2 or La2O3 was significant for NO conversion. XPS results showed that the electron density around Pd was increased by CeO2 and/or La2O3, the binding energy of Pd 3d decreased as the order: Pd/Al>Pd/Ce/Al>Pd/La/Al>Pd/CeLa/Al. The electron-rich Pd showed Rh-like catalytic properties which exhibited good activity for the reduction of NO. NO-TPD results showed that the addition of CeO2 and/or La2O3 increased NO adsorption on surface, and promoted the conversion of NO.     

Drastic increase of selectivity for H2O2 formation in direct oxidation of H2 to H2O2 over supported Pd catalysts due to their bromination

Incorporation of bromide anions (1.0 wt%) in supported Pd catalysts (viz. Pd supported on Al2O3, ZrO2, SiO2, H-beta or Ga2O3) leads to a drastic increase in their selectivity for H2O2 formation in the direct oxidation of H2 to H2O2 by O2(at room temperature) in an aqueous acidic (0.03 M H3PO4) reaction medium; the selectivity increase is accompanied by a large decrease in the H2O2 decomposition activity of the catalysts.     

Development of magnetic,ferrite supported palladium catalysts for 2,4-dinitrotoluene hydrogenation

Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe₂O₄, Pd/CuFe₂O₄, Pd/NiFe₂O₄) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe₂O₄ catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe₂O₄ catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.     

有机高分子固载钯催化剂的羰基化和加氢催化性能

本文利用耐温性能较好的主链上含有多个配位原子(N,O)能成膜的直链高分子杂环联苯聚醚酮(PEK),带酚酞侧基的聚醚砜(PES-C)和两种聚酰亚胺(PCK和PIK)为载体固载PdCl~2,制备了高分子固载钯催化剂。研究了它们在烯丙基溴的常压羰基化反应和1-辛烯的常压加氢反应中的催化性能。考察了催化剂的制备方法、Pd含量、溶剂和高分子的主链结构对催化剂活性的影响。催化剂Pd-PEK(Ⅰ) (Pd wt%=0.22%)和Pd-PES-C(Ⅱ)(Pd wt%=0.28%)在温和的条件下对上述两反应都表现出了很高的催化活性。在极低的Pd含量(Pd wt%=0.04%)时,催化剂Pd-PES-C(Ⅲ)显示出了特别高的初活性,TOF~m~a~x分别达345mol CO/mol Pd·min和493mol H~2/mol Pd·min。实验结果表明制备方法等因素对催化剂的活性有很大的影响。     

Doping of Ceria-Zirconia Solid Solution with Rare-earth Elements

The increasingly restrictive regulations on car exhaust emissions will necessitate the development of a new generation of three way catalysts (TWC) with better performance1. Ceria (CeO2) is the main component of the current TWC: its key role is to compensate the fluctuations in the exhaust stream composition, therefore, allowing to expand the air/fuel(A/F) operating window of catalytic converters2. This property is related to its oxygen storage capacity (OSC), associated to the redox couple Ce4+/Ce3+. However, CeO2 alone is easy to sinter to lost OSC at high temperature3.Ceria-zirconia (CexZr1-xO2) solid solutions by incorporation of Zr4+ in the CeO2 lattice have enhanced OSC and greater thermal stability, which are becoming the key materials for the new generation of TWC4. OSC of ceria-zirconia solid solutions can be further improved by the addition of M3+ dopants5. Besides Ce, other rare-earth elements such as Pr and Tb can vary their oxidation state. Pr and Tb are particularly suitable for making solid solutions with cerium because the known structure of PrO2 and TbO2 is of the cubic fluorite type, and the ionic radii of Pr4+ and Tb4+ are close to that of Ce4+6.In this paper, Ce0.6Zr0.3M0.1O2 (M=Y, La, Pr, Tb) were prepared by co-precipitation technique and characterized by a series of methods. Meanwhile, palladium-only TWCs were prepared by slurry coating and their catalytic activity was evaluated under the condition of simulated exhaust in the lab.XRD and FT-Raman spectra results show Ce0.6Zr0.3M0.1O2 have cubic fluorite structure which keep unchanging at high temperature. The different dopant ion radii brought different effect on the cell parameter of Ce0.6Zr0.3M0.1O2. The X-ray photoelectron spectroscopy (XPS) results show that the binding energy of Ce3d, Zr3d and O1s for Ce0.6Zr0.3M0.1O2 rose compared with that for Ce0.6Zr0.4O2, indicating dopant elements changed chemistry environment of solid solutions which was available to improve redox performance From TPR results, doping La can not change redox performance of solid solution, but doping Y decreased reduction temperature. Doping Pr and Tb notably improved redox performance of solid solutions due to appearance of low-temperature reduction peak in TPR profile which come from mobility of bulk oxygen.Compared with Pd/Ce0.6Zr0.4O2, doping Y and La unchanged A/F characteristic of TWCs, but doping Pr and Tb widen A/ F operating window and make HC, CO and NO have higher conversion.The light-off temperature of Pd/Ce0.6Zr0.3La0.1O2 was corresponded to that of Pd/Ce0.6Zr0.4O2.However, the light-off temperatures of Pd/Ce0.6Zr0.3M0.1O2 (M=Y, Pr, Tb) were lower than that of Pd/Ce0.6Zr0.4O2, which kept much lower after high temperature treatments. Among Pd/Ce0.6Zr0.3M0.1O2 (M=Y, La, Pr, Tb), Pd/Ce0.6Zr0.3Tb0.1O2 showed wider A/F operating window,higher conversion, lower light-off temperature and better high-temperature resistance     

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support

A mesoporous support based on silica and zirconia (ZS) was used to prepare monometallic 1 wt% Pd/ZS, 10 wt% Fe/ZS, and bimetallic FePd/ZS catalysts. The catalysts were characterized by TPR-H₂, XRD, SEM-EDS, TEM, AAS, and DRIFT spectroscopy of adsorbed CO after H₂ reduction in situ and tested in hydrodechlorination of environmental pollutant 4-chlorophelol in aqueous solution at 30 °C. The bimetallic catalyst demonstrated an excellent activity, selectivity to phenol and stability in 10 consecutive runs. FePd/ZS has exceptional reducibility due to the high dispersion of palladium and strong interaction between FeOx and palladium, confirmed by TPR-H₂, DRIFT spectroscopy, XRD, and TEM. Its reduction occurs during short-time treatment with hydrogen in an aqueous solution at RT. The Pd/ZS was more resistant to reduction but can be activated by aqueous phenol solution and H₂. The study by DRIFT spectroscopy of CO adsorbed on Pd/ZS reduced in harsh (H₂, 330 °C), medium (H₂, 200 °C) and mild conditions (H₂ + aqueous solution of phenol) helped to identify the reasons of the reducing action of phenol solution. It was found that phenol provided fast transformation of Pd⁺ to Pd⁰. Pd/ZS also can serve as an active and stable catalyst for 4-PhCl transformation to phenol after proper reduction.     

Comparative study of catalytic activity of Pd loaded hydroxyapatite and fluoroapatite in butan-2-ol conversion and methane oxidation

Palladium loaded calcium-hydroxyapatite, Pd(z)/CaHAp, and calcium-fluoroapatite, Pd(z)/CaFAp, were synthesised and characterised by TEM, XRD, IR and UV–vis–NIR spectroscopies. Introduction of palladium does not change the structure of CaHAp and CaFAp. The average size of PdO particles was found to be around 4–5 nm on Pd(1)/CaHAp but larger (6–7 nm) on Pd(1)/CaFap. The acid–base properties of the supports and of the catalysts were studied using butan-2-ol conversion. On CaHAp and CaFAp, the butenes yield (dehydration reaction) is very low either in the absence or in the presence of oxygen. The methyl ethyl ketone yield (dehydrogenation reaction) is significant only in the presence of oxygen and higher over CaFAp. Conversely, the performances of Pd(z)/CaHAp are better than those of Pd(z)/CaFAp below 180 °C. Above 180 °C, buta-2-ol combustion is favoured on Pd/CaHAp but not on Pd/CaFAp.

In methane oxidation, Pd(z)/CaHAp showed also a much larger activity than Pd(z)/CaFAp. On 2 wt% Pd loaded CaHAp, the methane oxidation reaches a conversion of almost 100% at 350 °C, which is comparable with the performance of conventional Pd/Al₂O₃ catalysts. The reducibility of PdO under methane–oxygen mixtures is lower on Pd(z)/CaHAp. For both reactions, the lower activity of Pd(z)/CaFAp is related to its higher acidity, resulting from the substitution of OH⁻ by F⁻, and to the larger PdO particle size.     

Determination of Ag, Cd, Pb, Zn and Pd in sea-water by thermal-ionization isotope-dilution mass spectrometry

The concentrations of Ag, Cd, Pb, Zn and Pd in sea-water have been determined by thermal-ionization isotope-dilution mass spectrometry. The concentrations found, in ng/kg, were 0.6 +/- 0.4 Ag, 1.9 +/- 0.4 Cd, 18 +/- 8 Pb, 30 +/- 8 Zn and < 4 Pd. These levels are lower than some reported previously. Determination of Pd in sea-water is reported for the first time.     

负载Pd密偶催化剂的载体效应

采用尿素水解法或吸附沉淀法制备了金属氧化物载体,并用浸渍法负载0.5%Pd制得了Pd/Sn0.4Zr0.6O2,Pd/ZrO2,Pd/SnO2,Pd/SnO2-Al2O3和Pd/Al2O3催化剂.采用原位漫反射红外光谱、拉曼光谱、X射线光电子能谱和程序升温还原等方法对催化剂结构进行了表征,探讨了不同载体对表面PdOx物种化学吸附性质和氧化还原性能的影响,并与样品的丙烷氧化活性相关联.漫反射红外光谱表明,在Pd/SnO2-Al2O3中,Sn对Al2O3表面的Pd原子簇起到稀释作用,促进了Pd的分散,使得其CO线式吸附强度明显高于Pd/Al2O3,但Pd过高的分散度不仅减少了表面Pd-PdO活性位对的数目,而且使反应中间物种Pd-OH之间脱水困难,因而阻塞了活性位,降低了其循环氧化还原活性;而在Sn0.4Zr0.6O2复合氧化物载体中,SnO2有效地阻止了四方晶相ZrO2向稳态单斜晶相转变,且复合载体的比表面积较ZrO2和SnO2有所增加,其表面PdOx物种的分散度适中.此外,Sn0.4Zr0.6O2复合氧化物负载的Pd的价态介于Pd0与Pd2 之间,表面氧空位较多,促进了丙烷中C-H键的活化,使比表面积较低的Pd/Sn0.4Zr0.6O2具有最好的催化丙烷氧化能力,相反比表面积较高的Pd/SnO2-Al2O3活性很差,说明分散度适中且具有较低氧化态的PdOx(0相似文献   

（PdCl2—PVP）／Al2O3催化剂中Pd状态的探讨

氯化钯先锚定在聚乙烯吡咯烷酮上后进一步负载到Al_2O_3上所制的催化剂[简称(PdCl_2-PVP)/Al_2O_3]是一种活性、选择性高,稳定性好的烯烃、二烯烃和多烯烃加氢催化剂。本文结合加氢反应,使用XPS、FT-IR、电镜及用CO为探针的FT-IR,对这种催化剂进行了考察。实验说明,在这种催化剂中,钯的价态是在0—2之间。红外光谱在486cm~(-1)处有一微弱的小峰,说明存在Pd—N的配位键。催化剂中钯含量低时(0.2wt％)稳定性好,不吸附CO,活性中心是络合钯原子;当钯含量较高时(0.7wt％),催化剂的初活性虽不低,稳定性却较差,这种催化剂能吸附CO,IR谱图上仅在1919cm~(-1)处有CO桥式吸附态的伸缩振动。表明除络合钯原子外,还有聚集的钯金属存在。FT-IR尚表明,PVP在Al_2O_3上可能并非单纯的物理吸附。电镜结果表明,PVP在Al_2O_3上呈30—70(?)的微球状,(PdCl_2-PVP)/Al)_2O_3上的(PdCl_2-PVP)亦呈微球状,与前者无明显区别,这种催化剂中其活性中心是络合钯原子。     

In situ ATR-IR study of prochiral 2-methyl-2-pentenoic acid adsorption on Al2O3 and Pd/Al2O3

Adsorption and desorption of trans-2-methyl-2-pentenoic acid (MPeA) in dichloromethane (CH(2)Cl(2)) were investigated by using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. A liquid flow-through spectroscopic cell allowed for high quality spectra to be obtained from deposited thin films of Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) on a ZnSe internal reflection element. The MPeA molecules adsorb on both Al(2)O(3) and Pd surfaces molecularly and dissociatively under the concentration range examined (2-16 mM). In the case of molecular adsorption, both monomer (ν(C=O) ~ 1720 cm(-1)) and dimer (ν(C=O) ~ 1685 cm(-1)) species are observed to adsorb, with the relative amount of monomer to dimer dependent on the surface and the liquid phase acid concentration. In the case of dissociative adsorption, the acid adsorbs predominantly in a bridged bidentate configuration, as adjudged by the ca. 150-220 cm(-1) separation between asymmetric and symmetric vibrational bands. All of these species are found to be strongly adsorbed on both Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) surfaces, even under pure solvent flow after adsorption.     

Extraction equilibrium of palladium(II) with 2-methyl-8-quinolinol into supercritical carbon dioxide fluid

The present study is concerned with the extraction behavior and equilibrium of Pd(II) with 2-methyl-8-quinolinol (HMQ) into supercritical fluid CO(2) (SF-CO(2)). Pd(II)-HMQ complex extracted from a weakly acidic solution (pH 2-3) into SF-CO(2) was determined to be Pd(MQ)(2) on the basis of a slope analysis. The extraction constant K(ex,SF) (=[Pd(MQ)(2)](SF)[H(+)](2)[Cl(-)](4)[PdCl(4)(2-)](-1)[HMQ](-2)) was determined to be 10(4.3+/-0.2) at 8.5 MPa, 45 degrees C and I=0.4 M (H,Na)Cl (1 M=1 mol dm(-3)). The distribution behavior of HMQ between an aqueous and a SF-CO(2) phase was examined so as to discuss quantitatively the extraction equilibrium. The extraction constant (K(ex,Cy)) of Pd(II) with HMQ into cyclohexane with a similar polarity to SF-CO(2) was determined and the K(ex,SF) was compared with the K(ex,Cy). Pd(II) at the concentration range of 10(-5)-10(-4) M in the aqueous solution (pH<3) containing relatively high concentration of chloride ion was found to be extracted efficiently by the SF-CO(2) extraction.     

Functionalized cellulose-preyssler heteropolyacid bio-composite: An engineered and green matrix for selective,fast and in–situ preparation of Pd nanostructures: synthesis,characterization and application

A new and green engineered biocomposite was synthesized by sol–gel method, using different loadings of the Preyssler heterpolyacid (8, 15, 25, 40 and 50 wt%) on the functionalized microcrystaline cellulose surface. For the first time, this two-component polymeric biocomposite used for in-situ catalytic synthesis of Pd nanoparticles with the aim of producing tricomponent nanobiocomposites. Preyssler loading on the functionalized surface, controled the size and shape of Pd nanoparticles, time, and pH of their formation. All biocomposites and nanobiocomposites were characterised by FTIR, XRD, BET, TGA, SEM, EDS and TEM. The SEM analysis for two component polymeric biocomposites confirmed the presence of the Preyssler on the surface of functionalized cellulose. The formation of Pd nanoparticles on the surface, was observed by color changing (yellow to deep brown) and confirmed by UV–visible spectroscopy. The Pd nanoparticles formation was fast (2–4 min) for 8 wt% in pH = 2–3 at 80 °C. TEM analysis illustrated the spherical Pd nanoparticles with a size of 5–20 nm, at the lowest loading of Preyssler, and rod shapes with a size of 30–40 nm at the highest loading. The obtained nanobiocomposite exhibited high catalytic activity for the decolourisation of tartrazine, as a model of dyes pollutant in the industry with high degradation efficiency. The catalytic reactions were extended with other azo dyes including methyl orange and rodamine B.     

Influence of Pd precursors on the catalytic performance of Pd–H4SiW12O40/SiO2 in the direct oxidation of ethylene to acetic acid

The effects of palladium precursors (PdCl₂, (NH₄)₂PdCl₄, Pd(NH₃)₂Cl₂, Pd(NO₃)₂ and Pd(CH₃COO)₂) on the catalytic properties in the selective oxidation of ethylene to acetic acid have been investigated for 1.0 wt% Pd–30 wt% H₄SiW₁₂O₄₀/SiO₂. The structures of the catalysts were characterized using X-ray diffraction, N₂ adsorption, H₂-pulse chemical adsorption, infrared spectrometry of the adsorbed pyridine, H₂ temperature-programmed reduction and X-ray photoelectron spectroscopy. The present study demonstrates that the different palladium precursors can lead to the significant changes in the dispersion of palladium. It is found that Pd dispersion decreases as follows: PdCl₂ > (NH₄)₂PdCl₄ > Pd(NO₃)₂ > Pd(NH₃)₂Cl₂ > Pd(C₂H₃O₂)₂, which is nearly identical to the catalytic activity. This indicates that the dispersion of palladium plays an important role in the catalytic activity. Furthermore, density of Lewis (L) and Brönsted (B) acid sites are also strongly dependent on the palladium precursors. It is also demonstrated that an effective catalyst should possess a well combination of Brönsted acid sites with dispersion of palladium.     

Preparation and characterization of Pd modified CeO2 nanoparticles for photocatalytic degradation of dye

The aim of this work was to investigate the structural and optical properties of bare cerium dioxide (CeO₂) and Pd-doped CeO₂ (0.5, 1.0, 1.5 and 2.0 wt%) photocatalysts prepared by a combination of homogeneous precipitation and the impregnation method. X–ray diffraction analysis indicated that all samples were composed of the cubic fluorite phase of CeO₂. Scanning electron micrographs revealed that all samples provided mostly spherical morphology with high agglomeration and estimated particle sizes ranging from 10 to 20 nm in diameter. The XPS core-level spectra of Pd species after incorporating 2.0 wt% Pd–doped CeO₂ showed double peaks with binding energies of Pd3d_5/2 and Pd3d_3/2 corresponding to the Pd²⁺ oxidation state. The results from diffuse reflectance UV–visible spectroscopy showed that doping with Pd increased the absorbance onset of CeO₂ to a longer wavelength, while the band gap decreased from 3.0 eV to 2.8 eV with 2.0% Pd doping concentration. This was likely due to the creation of impurity levels of Pd²⁺ inside the conduction and valence bands of CeO₂. The photoluminescence spectra (PL) indicated that the emission peak intensity of CeO₂ decreased in the presence of Pd²⁺ dopant in CeO₂. This was associated with a decrease in the electron–hole recombination rate for electronically-excited. Photocatalytic activity for methyl orange dye degradation under visible light irradiation of 1.0 wt% Pd–doped CeO₂ was determined as the optimal doping level with photocatalytic activity 5 times higher than that of bare CeO₂ photocatalyst.     

Structural changes of Pd13 upon charging and oxidation/reduction

First-principle generalized gradient corrected density functional calculations have been performed to study the stability of cationic and anionic Pd(13) (+∕-), and neutral Pd(13)O(2) clusters. It is found that while cationic Pd(13) (+) favors a C(s) geometry similar to the neutral Pd(13), both anionic Pd(13)(-) and neutral Pd(13)O(2) favor a compact ~I(h) structure. A detailed analysis of the electronic structure shows that the stabilization of the delocalized 1P and 2P cluster orbitals, and the hybridization of the 1D orbitals with the oxygen atomic p orbitals play an important role in the energetic ordering of C(s) and ~I(h) isomers. A structural oscillation is predicted during an oxidation/reduction cycle of Pd(13) in which small energy barriers between 0.3 and 0.4 eV are involved.     

Superelectrophilic tetrakis(carbonyl)palladium(II)- and -platinum(II) undecafluorodiantimonate(V), [Pd(CO)4][Sb(2)F(11)]2 and [Pt(CO)4][Sb(2)F(11)]2: syntheses, physical and spectroscopic properties, their crystal, molecular, and extended structures, and density functional calculations: an experimental, computational, and comparative study .

The salts [M(CO)(4)][Sb(2)F(11)](2), M = Pd, Pt, are prepared by reductive carbonylation of Pd[Pd(SO(3)F)(6)], Pt(SO(3)F)(4) or PtF(6) in liquid SbF(5), or HF-SbF(5). The resulting moisture-sensitive, colorless solids are thermally stable up to 140 degrees C (M = Pd) or 200 degrees C (M = Pt). Their thermal decompositions are studied by differential scanning calorimetry (DSC). Single crystals of both salts are suitable for an X-ray diffraction study at 180 K. Both isostructural salts crystallize in the monoclinic space group P2(1)/c (No. 14). The unit cell volume of [Pt(CO)(4)][Sb(2)F(11)](2) is smaller than that of [Pd(CO)(4)][Sb(2)F(11)](2) by about 0.4%. The cations [M(CO)(4)](2+), M = Pd, Pt, are square planar with only very slight angular and out-of-plane deviations from D(4)(h)() symmetry. The interatomic distances and bond angles for both cations are essentially identical. The [Sb(2)F(11)](-) anions in [M(CO)(4)][Sb(2)F(11)](2,) M = Pd, Pt, are not symmetry-related, and both pairs differ in their Sb-F-Sb bridge angles and their dihedral angles. There are in each salt four to five secondary interionic C- -F contacts per CO group. Of these, two contacts per CO group are significantly shorter than the sum of the van der Waals radii by 0.58 - 0.37 A. In addition, structural, and spectroscopic details of recently synthesized [Rh(CO)(4)][Al(2)Cl(7)] are reported. The cations [Rh(CO)(4)](+) and [M(CO)(4)](2+), M = Pd, Pt, are characterized by IR and Raman spectroscopy. Of the 16 vibrational modes (13 observable, 3 inactive) 10 (Pd, Pt) or 9 (Rh), respectively, are found experimentally. The vibrational assignments are supported by DFT calculations, which provide in addition to band positions also intensities of IR bands and Raman signals as well as internal force constants for the cations. (13)C NMR measurements complete the characterization of the square planar metal carbonyl cations. The extensive characterization of [M(CO)(4)][Sb(2)F(11)](2), M = Pd, Pt, reported here, allows a comparison to linear and octahedral [M(CO)(n)()][Sb(2)F(11)](2) salts [M = Hg (n = 2); Fe, Ru, Os (n = 6)] and their derivatives, which permit a deeper understanding of M-CO bonding in the solid state for superelectrophilic cations with [Sb(2)F(11)](-) or [SbF(6)](-) as anions.     

Pd/C催化剂用于CO2电化学还原生成CO:Pd载量的影响

CO₂电化学还原反应可以将CO₂转化为燃料并同时实现再生能源的有效存储. 目前纳米结构的多相催化剂已经广泛应用于此反应,其中碳负载钯纳米粒子（Pd/C）表现出优异的CO₂电化学还原性能. 本工作研究了钯载量对于Pd/C催化剂结构以及其催化CO₂还原生成CO反应活性和选择性的影响. 不同载量的Pd/C催化剂通过液相还原方法制备,钯纳米粒子均匀地分散在碳载体上,载量并没有明显改变对纳米粒子的粒径. 在优选的电解质（0.1 mol·L^-1 KHCO₃）中,CO法拉第效率与载量呈现火山型曲线关系,-0.89 V时载量为20wt%的Pd/C催化剂达到最高的CO法拉第效率(91.2%). 生成CO的几何电流密度随着钯载量的增加而增加,但CO转换频率具有相反的趋势,载量为2.5wt%的Pd/C催化剂具有最高的转换频率. 这种载量对CO₂电化学还原反应活性和选择性的影响主要由活性位的数量、反应动力学、中间物种的稳定性以及反应物、中间物种和产物的传质过程等共同决定.