Characterization of VOx-TiO2 catalysts and their activity in the partial oxidation of methyl ethyl ketone

The present work focuses on the partial oxidation of methyl ethyl ketone to acetic acid over TiO₂ supported vanadia catalysts with V loadings from 1 to 13.5 wt.%. In order to elucidate the relation between catalytic activity and the structure of the catalysts, the catalysts were also characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction with hydrogen (TPR), and temperature programmed desorption of lattice oxygen (TPD-O₂). The investigations show that with increasing V loading the MEK conversion increased whereas the turn-over frequency decreased. At lower V loading (1–4 wt.%) the total oxidation to CO_x was favoured and the selectivities to acetic acid and other oxygenated products were low. The highest selectivities to acetic acid were achieved at V loadings of 4–6 wt.%. Based on literature data and our results, a scheme of the reaction pathways for the partial oxidation of MEK to AcOH and other by-products was developed.     

HPW and supported HPW catalyzed condensation of aromatic aldehydes with aniline: Synthesis of DATPM derivatives

The mesoporous Si-MCM-41 was synthesized by hydrothermal method and various wt.% (20 and 30 wt.%) of HPW were loaded on Si-MCM-41 by wet impregnation method. The synthesized Si-MCM-41 and HPW-loaded catalysts were characterized by XRD, BET surface area, FT-IR, TEM and TGA–DTG techniques. The catalytic activity of the catalyst was tested over the condensation reaction of aniline with various aromatic aldehydes at refluxing temperature under liquid-phase condition, which yields highly commercial product namely diamino triphenyl methanes (DATPMs). The effects of various parameters like catalyst, mole ratio, solvents and substituent effect on the formation of DATPMs were optimized. The catalytic activity of the catalysts showed the following order: H₃PW₁₂O₄₀·nH₂O > H₃PMo₁₂O₄₀·nH₂O > H₄SiW₁₂O₄₀·nH₂O > 20 wt.% HPW/MCM-41 > 30 wt.% HPW/MCM-41 > HM (12) > Hβ (8) > HY (4) > HZSM-5 (15) > Al-MCM-41 (25). The results showed that mole ratio of 4:1 (aniline:aldehyde) gave higher yield than the other mole ratios. Acetonitrile and ethyl acetate shows better activity especially in the supported materials than toluene was used as a solvent. The product thus obtained was analyzed by ¹H NMR, FT-IR techniques.     

Characterization and catalytic-hydrogenation behavior of SiO2-embedded nanoscopic Pd, Au, and Pd-Au alloy colloids

Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au colloids, and pure Pd and Au colloids stabilized with tetraalkylammonium bromide following a modified sol-gel procedure with tetrahydrofuran (THF) as the solvent. Tetraethoxysilicate (TEOS) was used as the precursor for the silica support. The molar composition of the sol was TEOS/THF/H2O/HCl = 1:3.5:4:0.05 for the bimetallic Pd-Au and TEOS/THF/H2O/HCl = 1:4.5:4:0.02 for Pd and Au monometallic systems. After refluxing, the colloid was added as a 4.5 wt % solution in THF for Pd-Au, 10.2 wt % solution in THF for Pd and 8.4 wt % solution in THF for Au at room temperature. The gelation was carried out with vigorous stirring (4 days) under an Ar atmosphere. Following these procedures, bimetallic Pd-Au-SiO2 catalysts with 0.6 and 1 wt % metal, and monometallic Pd- and Au-SiO2 catalysts with 1 wt % metal were prepared. These materials were further treated following four different routes: 1) by simple drying, 2) in which the dried catalysts were calcined in air at 723 K and then reduced at the same temperature, 3) in which they were directly reduced in hydrogen at 723 K, and 4) in which the surfactant was extracted using an ethanol-heptane azeotropic mixture. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption measurements, solid-state 1H, 13C, 29Si-CP/MAS-NMR spectroscopy, powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and 197Au M?ssbauer spectroscopy. The physical characterization by a combination of these techniques has shown that the size and the structural characteristics of the Pd-Au colloid precursor are preserved when embedded in an SiO2 matrix. Catalytic tests were carried out in selective hydrogenation of 3-hexyn-1-ol, cinnamaldehyde, and styrene. These data showed evidence that alloying Pd with Au in bimetallic colloids leads to enhanced activity and most importantly to improved selectivity. Also, the combination of the two metals resulted in catalysts that were very stable against poisoning, as was evidenced for the hydrogenation of styrene in the presence of thiophene.     

Comparative studies of gold catalysts prepared via solvated metal atom impregnation and conventional impregnation: characterization and low-temperature co oxidation

Supported Au catalysts for low-temperature CO oxidation were prepared by solvated metal atom impregnation (SMAI) and conventional impregnation (CI). X-ray photoelectron spectroscopy investigations indicated that gold in all the samples was in the metallic state. TEM and XRD measurements showed that the mean diameter of Au particles prepared by SMAI was smaller than that of those prepared by CI with the same gold content. Catalytic tests showed that SMAI catalysts had higher CO oxidation activity than CI catalysts with the same compositions. Both SMAI and CI Au/TiO₂catalysts exhibited high activities in low temperature CO oxidation. Full CO conversion was obtained at 323 K for 3.1 wt.% Au/TiO₂ (SMAI) catalyst, which displayed higher activity than the 3.1 wt.% Au/D-72(SMAI) and 3.1 wt.% Au/TiO₂(CI). Although the sizes of gold particles prepared by the same method and supported on both TiO₂ and resin were comparable, the Au/TiO₂ catalysts showed significantly higher activities than the Au/resin catalysts with the same Au contents under the same reaction conditions. These results prove that not only the gold particle size, but also the support plays a key role in CO oxidation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Transformation of 5-hydroxymethylene-5H-6,7-dihydrodibenzo[a,c]cyclohepten-6-one over Ru-containing BEA zeolites

Ru–BEA catalysts with 1.0–2.5 wt.% Ru were prepared by ion exchange. The acidic properties of these catalysts were investigated using deuterated acetonitrile, pyridine, and 2,6-di-tert-butyl-pyridine. The deposited Ru was studied by CO-FTIR spectroscopy. The materials were tested as catalysts in the hydrogenation of a conjugated cyclic keto–enol, namely, 5-hydroxymethylene-5H-6,7-dihydrodibenzo[a,c]cyclohepten-6-one. Beside hydrogenation, hydrogenolysis products were identified by GC–MS and ¹H NMR techniques. Relations were sought between the selectivity and some physicochemical properties of the catalyst.     

An Effect of a Support Nature and Active Phase Morphology on Catalytic Properties of Ni-Containing Catalysts in Hydrogenation of Biphenyl

Ni/Sup catalysts were prepared, where SBA-15, γ-Al₂O₃, SiO₂ were used as supports (Sup). The synthesized catalysts were investigated by the methods of low-temperature nitrogen adsorption, temperatureprogrammed reduction (TPR), and high-resolution transmission electron microscopy. The catalytic properties of the prepared catalysts were tested in liquid phase hydrogenation of biphenyl under conditions of a flow installation at temperatures of 60–100°C, pressure of 4 MPa, volumetric feed rate of 4–10 h^–1 and H₂: feed ratio of 1500 nM.. A 1 wt % solution of biphenyl in heptane,, as a model mixture, was used. It has been established that the activity of nickel hydrogenation catalysts depends on the nickel content and the type of support. The activity of supported nickel catalysts decreases in the series Ni-12/SBA-15 > Ni-12/SiO₂ >> Ni-12/Al₂O₃. The kinetic characteristics of the biphenyl hydrogenation reaction were determined: the rate constants and activation energy for the hydrogenation of the first and second aromatic rings of the substrate molecule.     

Liquid phase mononitration of chlorobenzene over WOx/ZrO2: A study of catalyst and reaction parameters

To study the effect of W concentration and activation temperature of the catalysts a series of WO_x/ZrO₂ samples with varying concentration of W (10–25 wt.%) were prepared and activated at 650/750 °C. XRD of sample shows 15 wt.% W stabilizes the tetragonal phase of zirconia up to 750 °C. Above and less than 15 wt.% shows peaks corresponding to monoclinic WO₃ and monoclinic ZrO₂, respectively. Further, the tungsten modification stabilizes the specific surface area of ZrO₂. There is an increase in the surface area observed up to 15 wt.% W, which declines on further increase in the concentration. The NH₃ TPD confirms the presence of acid sites with varying strength from the broad desorption profile. The 15 wt.% W and activated at 750 °C shows maximum acidity. The results of the nitration reaction of chlorobezene imply the 15 wt.% W and activation at 750 °C shows maximum activity. Not only yield, a better para-selectivity is also achieved with WO_x/ZrO₂ samples. Effect of activation temperature, W concentration and reaction parameters such as reaction temperature, reaction time, the presence of solvent and solvent free medium on activity and selectivity are studied in details.     

Performance of Pt/SnO2 catalyst in the gas phase hydrogenation of crotonaldehyde

Selective hydrogenation of crotonaldehyde was performed on 5% Pt/SnO₂ catalysts, in gaseous phase, at atmospheric pressure, at 353 K. Two types of catalyst were prepared using H₂PtCl₆ and Pt(NH₃)₄(NO₃)₂ as metallic precursors. Their performances were compared as a function of the reduction temperature and both catalysts were characterised by X-ray diffraction after different reduction treatments. Using the ex-chloride catalyst, the selectivity values to the unsaturated alcohol (UOL) resulted into a maximum of 45% while a selectivity as high as 70–77%, in 0–25% conversion range, was achieved by using ex-nitrate catalyst reduced at 443 K. The formation of Pt–Sn alloy on the metal particles of platinum was thought to be necessary to improve the activity and the selectivity on these catalysts. In the contrast, a presence of PtSn₂ formed at a reduction temperature higher than 473 K led to a decrease of activity and selectivity.     

Facile and Large-Scale Fabrication of Sub-3 nm PtNi Nanoparticles Supported on Porous Carbon Sheet: A Bifunctional Material for the Hydrogen Evolution Reaction and Hydrogenation

Facile and large-scale preparation of materials with uniform distributions of ultrafine particles for catalysis is a challenging task, and it is even more difficult to obtain catalysts that excel in both the hydrogen evolution reaction (HER) and hydrogenation, which are the corresponding merging and splitting procedures of hydrogen, respectively. Herein, the fabrication of ultrafine bimetallic PtNi nanoparticles embedded in carbon nanosheets (CNS) by means of in situ self-polymerization and annealing is reported. This bifunctional catalyst shows excellent performance in the hydrogen evolution reaction (HER) and the hydrogenation of p-nitrophenol. Remarkably PtNi bimetallic catalyst with low metal loading (PtNi₂@CNS-600, 0.074 wt % Pt) exhibited outstanding HER activity with an overpotential as low as 68 mV at a current density of 10 mA cm⁻² with a platinum loading of only 0.612 μg_Pt cm⁻² and Tafel slope of 35.27 mV dec⁻¹ in a 0.5 m aqueous solution of H₂SO₄, which is comparable to that of the 20 % Pt/C catalyst (31 mV dec⁻¹). Moreover, it also shows superior long-term electrochemical durability for at least 30 h with negligible degradation compared with 20 % Pt/C. In addition, the material with increased loading (mPtNi₂@CNS-600, 2.88 % Pt) showed robust catalytic activity for hydrogenation of p-nitrophenol at ambient pressure and temperature. The catalytic activity towards hydrogen splitting is a circumstantial evidence that agrees with the Volmer–Tafel reaction path in the HER.     

Influence of the Charge Transfer Capacity of Alkali and Alkaline Earth Metals as Promoters in Thehydrogenation of Phenol over Palladium and Nickel Catalysts

The gas phase hydrogenation (523-573 K) of phenol has been studied over 1 wt.% Pd/Al₂O₃ and 1 wt.% Ni/SiO₂ catalysts doped with Group I and II promoter oxides. A direct correlation between catalytic activity and the charge transfer capacity of the promoters is presented where hydrogenation is favored by increasing electron donation from the promoter. The Pd catalysts generated cyclohexanone (selectivity > 97%) as the predominant product; selectivity was unaffected by the presence of the alkali or alkaline earth dopants. The Ni system exhibited appreciable hydrogenolysis behavior and charge transfer from the dopants limited the degree of hydrodeoxygenation to favor complete hydrogenation to cyclohexanol.     

Ordered mesoporous silicates of MCM-41 type as support of pt catalysts for the enantioselective hydrogenation of 1-phenyl-1,2-propanedione

Summary Platinum catalysts (1 wt.%) supported on MCM-41 type and SiO₂have been prepared, characterized and evaluated in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298 K and 20 bar of hydrogen pressure, using cinchonidine (CD) as chiral modifier. Chemisorption and TEM results revealed that both catalysts posses similar metal dispersion, however, significant differences in the catalytic behavior were observed. With dichloromethane as solvent, high hydrogenation rates and ee values around 47% were obtained for the Pt/MCM-41 catalyst. This fact is attributed to a confinement effect. The initial reaction rate is strongly dependent on the CD concentration, and the reaction rate (or ee) vsCD concentration plot exhibits bell-type curves. The main products were (R) -1-hydroxy-1-phenylpropanone and (S) -1-hydroxy-1-phenylpropanone.</o:p>     

NiMoW/P-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Hydrotreating Catalysts: Influence of the Mo/W Ratio on the Hydrodesulfurization and Hydrogenation Activity

A series of NiMoW/P-Al₂O₃ catalysts with different Mo/W ratios (sample containing Mo only, Mo/W = 2: 1, Mo/W = 1: 1, Mo/W = 1: 2, and sample containing W only; P₂O₅ content of the support 2.0 wt %) were synthesized. The precursors of the active phase were the heteropoly acids H₃PMo₁₂O₄₀?nH₂O and H₃PW₁₂O₄₀?nH₂O, and also nickel citrate. The sulfide phase in the samples was studied by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy; the catalytic activity of the samples in dibenzothiophene hydrodesulfurization and naphthalene hydrogenation was determined. For the dibenzothiophene hydrogenolysis in the presence of quinoline and naphthalene (content in the model mixture, wt %: dibenzothiophene 0.3, naphthalene 1.5, and quinoline 0.5), k_HDS for different samples is in the range 17.6–42.5 h^–1 at 275°C and 24.6–45.9 h^–1 at 300°C. For the naphthalene hydrogenation, k_HYD varies from 0.79 to 1.89 h^–1 at 275°C and from 0.91 to 3.78 h^–1 at 300°C. The sample based on molybdenum showed the highest activity in hydrogenation and hydrodesulfurization.     

Formation of C4 Oligomers in Hydrogenation of Acetylene over Pd/Al2O3 and Pd/TiO2 Catalysts

Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/-alumina and 0.5 wt.% Pd/TiO₂catalysts. Non-steady-state regime of catalyst operation was tested in pulse-flow experiments. Significant carbon poisoning appears to be a necessaryrequisite for selective formation of ethylene. The effect of hydrogen and acetylene partial pressure has been tested on the selectivity of C₄products. At 273–298 K the catalysts showed 26–35% selectivity for C₄ hydrocarbons and <2.5% for ethane production at conversionsof 30–40%. Deuterium distribution in ethylene and 1,3-butadiene and the deuterium content of the surface hydrogen pool have been compared and mechanismof diene formation has been discussed.     

Effect of rare earths on selective hydrogenation of p-chloronitrobenzene over PtMOx/CNTs catalysts

The effect of rare earths(Sm,Pr,Ce,Nd and La)on the hydrogenation properties of p-chloronitrobenzene(CNB)over Pt/CNTs catalyst was studied in ethanol at 303 K and normal pressure.The results exhibited that the hydrogenation of p-CNB could be carded out over PtMOx/CNTs catalysts.Both catalytic activities and yields of p-chloroaniline(CAN)were all improved.PtCeOx/ CNTs catalyst exhibited the best catalytic activity(TOF was 0.47 s~(-1))and the highest yield of p-CAN(97.5 mol%).PtCeOx/CNTs (1.0 wt%)catalyst ...     

金属载体强相互作用增强Au/TiO2催化剂在3-硝基苯乙烯选择性加氢反应的活性

自Haruta与Hutchings于上世纪八十年代末发现金纳米催化剂优异的反应活性以来,科研人员对金催化的应用领域进行了广泛而深入地研究.对金催化科学和应用领域的研究一直在进行.大量的研究表明,金催化剂在各种选择性氧化反应中具有优异的催化性能(高活性和高选择性).然而,在催化加氢反应中,尽管金催化剂相比于铂族金属显示出优越的选择性,但是由于金催化剂选择性加氢反应的活性较差,使其在选择性催化加氢反应中的应用受到了极大的限制.研究表明,金催化剂较弱的活化氢气能力是其催化加氢反应活性低的主要原因.研究发现,氢气活化的活性中心可能是界面、负价金、低配位的金原子等.金催化剂具有明显的载体效应,金属-载体之间的相互作用能够显著地改变金催化剂的催化性能.Tauster等研究发现,铂族金属与还原性载体之间存在强相互作用,能够引发载体包覆金属表面,并且使得电子从载体向金属迁移,导致金属带负电.受金属-载体强相互作用(SMSI)效应的启发,本文探究了Au/TiO2催化剂中SMSI对金催化剂加氢性能的影响.在H2或O2气氛下高温焙烧Au/TiO2,获得一系列金催化剂(Au/TiO2-TA,T为焙烧温度(oC):300、400、500和600;A为气氛:H2或O2).对比在3-硝基苯乙烯(3-NS)选择性加氢反应中的活性发现,Au/TiO2-500H的TOF值是Au/TiO2-500O的3.3倍;动力学测试表明,Au/TiO2-500H和Au/TiO2-500O的反应表观活化能分别为79.5和105.1 kJ/mol.这表明两类催化剂催化活性中心的结构存在差异.X射线光电子能谱测试结果表明,Au/TiO2-H样品中Au带部分负电,而Au/TiO2-O中Au显示为金属态.HAADF-STEM和EELS显示,Au/TiO2-H中Au NPs的表面有TiOx物种,增加了Au-TiO2的界面.EPR结果表明,Au/TiO2-H中存在表面Ti3+物种,而Au/TiO2-O样品中则没有.为确认加氢反应的活性中心到底是界面还是负价金物种,本文探究了不同温度下氢气处理的Au/TiO2的结构与性能的关系,发现Au/TiO2-300H/400H/500H催化剂都显示出较好的催化3-NS加氢活性,而Au/TiO2-600H虽然具有更多的负价金物种,但是3-NS选择性加氢反应的活性反而降低,因此,负价金不是活性中心.这是因为不同温度处理的Au/TiO2-H样品中,SMSI的强弱不同,在300、400、500 oC下,SMSI能够增加Au-TiO2的界面长度,从而增强了3-NS加氢反应的活性;而温度达到600 oC,SMSI效应太强,Au NPs被包覆更密实,导致Au/TiO2-600H的3-NS选择性加氢反应的活性下降.密度泛函理论计算表明,Au/TiO2-H样品具有更低的H2解离活化能以及氢转移活化能.氢氘交换反应也进一步验证了SMSI有利于H2的活化.     

Zirconia-supported phosphotungstic acid as catalyst for alkylation of phenol with benzyl alcohol

The liquid-phase alkylation of phenol with benzyl alcohol was carried out using zirconia-supported phosphotungstic acid (PTA) as catalyst. The catalysts with different PTA loadings (5–20 wt.% calcined at 750 °C) and calcination temperature (15 wt.% calcined from 650 to 850 °C) were prepared and characterized by ³¹P MAS NMR and FT-IR pyridine adsorption spectroscopy. The catalyst with optimum PTA loading (15%) and calcination temperature (750 °C) was prepared in different solvents. ³¹P MAS NMR spectra of the catalysts showed two types of phosphorous species, one is the Keggin unit and the other is the decomposition product of PTA and the relative amount of each depends on PTA loading, calcination temperature and the solvent used for the catalyst preparation. The catalysts with 15% PTA on zirconia calcined at 750 °C showed the highest Brönsted acidity. At 130 °C and phenol/benzyl alcohol molar ratio of 2 (time, 1 h), the most active catalyst, 15% PTA calcined at 750 °C gave 98% benzyl alcohol conversion with 83% benzyl phenol selectivity.     

Study of pyridine-modified platinum- and palladium-containing selective-hydrogenation catalysts on fiber-glass woven support

Experimental results on the influence exerted by pyridine additives on the selectivity of the process in which the styrene fraction is purified to remove the microscopic admixture of phenylacetylene at low (up to 30°C) temperatures by selective hydrogenation with catalysts on an aluminoborosilicate or silica matrix with filler-metals in the form of platinum or palladium are presented. It was shown that pyridine-modified catalysts in these systems are effective in the selective hydrogenation of phenylacetylene for purification of raw styrene. The modification of a platinum catalyst on the aluminoborosilicate support results in that a deep degree of purification (>95%) is achieved even at low (up to 50°C) temperatures. Use of catalysts composed of 0.160 wt % Pt and silica woven-glass fabric, modified with pyridine additives, leads to a substantially lower loss of styrene (from 0.48 to 0.31% in some cases) in the temperature range of 30–50°C. It was demonstrated that addition of substances containing a unshared electron pair can noticeably affect the selectivity of the process in which the styrene fraction is purified from its impurity content even in the order of 0.01%. Depending from the substrate composition and active filler-metal, the temperature, together with changing the support properties, exerts varied influence on modified metallic catalysts, which is manifested in change in the activation energy and, as a consequence, in that of the hydrogenation mechanism.     

Synergism of the catalytic effect of nanosized gold-nickel catalysts in the reaction of selective acetylene hydrogenation to ethylene

Gold and nickel nanoclusters immobilized on aluminum oxide exhibited high activity in the reaction of acetylene hydrogenation to ethylene with molecular hydrogen at temperatures from 20 to 64°C. The reaction selectivity on Au-Ni nanocomposites with metal concentrations from 0.02 to 0.36 wt % was no lower than 99.99%, and the stability of catalysts was retained for at least 12 h. The simultaneous presence of gold and nickel in the systems resulted in the synergism of their catalytic effects: acetylene conversion on layer-by-layer immobilized metal clusters was higher than the total conversion on individual gold and nickel clusters. The dependence of the conversion of acetylene on bimetallic catalysts on the Au : Ni ratio exhibited an extremal character.     

Liquid-phase alkylation of phenol with long-chain olefins over WOx/ZrO2 solid acid catalysts

The liquid-phase alkylation of phenol with 1-dodecene was carried out over WO_x/ZrO₂ solid acid catalysts. The catalysts were prepared by wet impregnation method using zirconium oxyhydroxide and ammonium metatungstate. Catalysts with different WO₃ loading (5–30 wt.%) were prepared and calcined at 800 °C and catalyst with 15% WO₃ was calcined from 700–850 °C. All the catalysts were characterized by surface area, XRD, and FTIR. The catalyst with 15% WO₃ calcined at 800 °C (15 WZ-800) was found to be the most active in the reaction. The effect of temperature, molar ratio and catalyst weight on dodecene conversion and products selectivity was studied in detail. Under the optimized reaction conditions of 120 °C, phenol/1-dodecene molar ratio 2 and time 2 h, the catalyst 15 WZ-800 gave >99% dodecene conversion with 90% dodecylphenol selectivity. Comparison of the catalytic activity of 15 WZ-800 with sulfated zirconia calcined at 500 °C (SZ-500) and Hβ zeolite showed that activity of SZ-500 was lower than that of 15 WZ-800, while Hβ zeolite showed negligible activity. It is observed that the presence of water in the reaction mixture was detrimental to the catalytic activity of WO_x/ZrO₂. The catalyst 15 WZ-800 also found to be an efficient catalyst for alkylation of phenol with long-chain olefins like 1-octene and 1-decene.     

Properties of Pd–Ag/C catalysts in the reaction of selective hydrogenation of acetylene

Samples of Pd/C and Pd–Ag/C, where C represents carbon nanofibers (CNFs), are synthesized by methane decomposition on a Ni–Cu–Fe/Al₂O₃ catalyst. The properties of Pd/CNF are studied in the reaction of selective hydrogenation of acetylene into ethylene. It is found that the activity of the catalyst in hydrogenation reaction increases, while selectivity decreases considerably when the palladium content rises. The obtained dependences are caused by the features of palladium’s interaction with the carbon support. At a low Pd content (up to 0.04 wt %) in the catalyst, the metal is inserted into the interlayer space of graphite and the catalytic activity is zero. It is established by EXAFS that the main share of palladium in catalysts of 0.05–0.1 wt % Pd/CNF constitutes the metal in the atomically dispersed state. The coordination environment of palladium atoms consists of carbon atoms. An increase in the palladium content in a Pd/CNF catalyst up to 0.3 wt % leads to the formation of highly dispersed (0.8–1 nm) Pd particles. The Pd/CNF samples where palladium is mainly in the atomically dispersed state exhibit the highest selectivity in the acetylene hydrogenation reaction. The addition of silver to a 0.1 wt % Pd/CNF catalyst initially probably leads to the formation of Pd–Ag clusters and then to alloyed Pd–Ag particles. An increase in the silver content in the catalyst above 0.3% causes the enlargement of the alloyed particles and the palladium atoms are blocked by a silver layer, which considerably decreases the catalytic activity in the selective hydrogenation of acetylene.