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In the present paper the final goal is to use the hydrogenolysis of hydrocarbons as a diagnostic tool for characterizing the metallic surface, i.e. to give a technique for drawing conclusions about the character of a metallic surface itself from the observed kinetic parameters. The main features are as follows: Surface properties of a transition metal are essentially determined by the electron structure and geometry of the bulk, members of the group VIII metals possess, therefore, apriori activity in the hydrogenolysis of a given hydrocarbon. Vulcano shaped curves observed in the hydrogenolysis of ethane, n-pentane, may, therefore, be an indication that neither too strong, nor too weak interaction between the catalyst surface and the substrate is good for the optimum catalyst performance. In addition to the ability of a metal in the “weak” to “strong” type of interconvension conceptualized earlier, the kinetic parameters may be influenced by some additional factors e.g. temperature, hydrogen pressure and the aging of the catalyst. A systematic change in the catalyst structure of platinum and ruthenium results in a characteristic variation in the activity of ethane and n-butane hydrogenolysis as well as in selectivity. By carefully analysing the limiting factors mentioned the effect of different supports, metallic dispersion, impregnating substrate, alloying with iron and rhenium and adsorbed sulphide on the activity and selectivity was determined.

Hydrogenation of acetylene has been investigated on Au-iron oxide catalysts containing 4.5, 3.0, 5.6 wt% Au prepared by deposition–precipitation (DP) with urea, adsorption of Au sol (SA) and by co-precipitation (CP) of HAuCl 4 and Fe(NO 3 ) 3 , respectively. The latter method produced Au particles supported on 2-line ferrihydrite (Fe 5 HO 8 ·4H 2 O). Au/iron oxide catalyst precursors (Au/α-Fe 2 O 3 and Au/2-line ferrihydrite) were characterized by BET, TGA, TPR and XRD, and the Au particle size by TEM measurements. The TPR measurements confirm the ease of transformation of 2-line ferrihydrite to magnetite (Fe 3 O 4 ) and that the formation of magnetite from α-Fe 2 O 3 depends strongly on the size of the gold and the supporting oxide particles. Particle size effect of gold has been investigated in semi-hydrogenation of acetylene. Temperature of hydrogen treatment has been observed to play a crucial role in the activity and ethylene selectivity. Au/FeO x samples hydrogen treated at 353–473 K prior to introduction of the reactants (H 2 :C 2 H 2 = 140, 0.11% C 2 H 2 ) show very limited over-hydrogenation (ethane formation is less than ≈1%) and 2–4% selectivity of oligomer (C4+) formation at 353–473 K. Hydrogen treatment of the samples at T > 573 K but lower than the wustite (FeO) stability point (≈843 K) resulted in partial reduction of Fe 3 O 4 and formation of Fe 0 . The shift of Au(1 1 1) XRD line to higher 2 Θ provided evidence for the incorporation of Fe 0 into the Au particles. Modification of the Au/Fe 2 O 3 perimeter and appearance of Fe 0 co-catalyst and Fe–Au ensembles on the surface increased the hydrogenation activity but decreased the selectivity of ethylene formation.

Acetylene hydrogenation has been investigated on 1.8 wt.% Au(I)/SiO2 and 1.9wt.% Au(II)/SiO2 catalysts prepared by fixation of Au sol to SiO2 (Aerosil 200). The mean particle size measured by TEM is 3.7 and 6.1 nm, respectively. For the sake of comparison a 2.1 wt.% Au/TiO2 sample was prepared by deposition-precipitation (DP) technique (mean particle size of Au is 3.3 nm). Transformation of acetylene was measured at 5 K/min ramp rate with gas mixtures containing the reactants at H2/C2H2=2 and 70 ratios. The C2H2 content of the gas mixture was 0.11% (0.11 kPa C2H2). The activity sequence at 423 K was: Au/TiO2>Au(I)/SiO2≫Au(II)/SiO2. Both the partial pressure of hydrogen and the temperature significantly affect the activity (acetylene conversion) and ethylene selectivity. Above 500–550 K over-hydrogenation (ethane formation) and hydrogenolysis (methane formation) decrease the ethylene selectivity. Faster deactivation and larger amount of deposit was observed on Au/TiO2 than on Au(I)/SiO2. A reaction scheme is proposed suggesting formation of sigma bonded intermediates as sp carbon hybridises to sp2 and sp3.

Various Pd shell thicknesses (0.12–1.5 nm) were synthesized on preformed Au particles of 5 nm size by seeded growth technique (15–80 at% Pd) using sodium citrate and tannic acid. The sols were characterized by UV–vis spectroscopy, TEM and high-resolution TEM (HRTEM) measurements. HRTEM confirmed the pseudomorphic growth of the Pd shell on the Au core. The Au/Pd core/shell particles were fixed onto SiO2 (Aerosil 200) support by PDDA polycation. The catalytic activity in acetylene hydrogenation and selectivity of competition between acetylene and propene were tested after O2 and H2 pretreatment. The samples even in “as prepared” state hydrogenated acetylene. The thin Pd layer (15–30 at% Pd) on Au provided higher hydrogenation activity than the thick Pd shell. However, thermal treatment of the samples in H2 stream causing Au/Pd intermixing shifted the activity maximum to higher Pd concentration (68–80 at% Pd). Comparison of the TOF (1/s) and selectivity values allowed us to conclude that the homogenized particle with 68–80 at% Pd shows better hydrogenation activity and selectivity than the thin Pd shell (15–30 at% Pd) on the Au core.

In the presence of pre-synthesized Au nanoparticles both pulse radiolysis and 2-propanol assisted reduction of Pd (II) chloride to palladium have been investigated with the intention to check the possible formation of Au–Pd heteroaggregates. Pulse radiolysis of Pd2+ (50 Gy dose/pulse at 298 K in 270 mM 2-propanol to scavange OH radicals) produced Pd nanoparticles of 3.9–2.5 nm depending on the citrate concentration (2.8–12 × 10−4 M). UV–vis measurements and TEM investigations confirmed that part of the Pd particles were attached to the Au particles of 28 ± 6 nm forming Au–Pd heteroaggregates. Hydrothermal treatment of Pd hydrosol at 363–395 K in the presence of Au nanoparticles was observed to facilitate formation of Pd tendrils on Au and 2D Pd structures by aggregation process. Reduction of Pd2+ with 2-propanol (1.55–2.2 M) in Au hydrosol and sodium citrate as capping agent was also tested at 348–353 K. At pH 3.5–4.5 reduction of Pd2+ resulted in an effective decoration of the gold particles with small crystals of Pd. The observed structures definitely differ from the usual Au/Pd core/shell nanoparticles. The Pd–Au samples were characterized by UV–vis, transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). Hydrogenation of 1,3-cyclooctadiene in the liquid phase was applied for the additional characterization of the structurally different samples.

Pd hydrosol was synthesized by reducing PdCl2 solution with dissolved H2 in the presence of PDDA [poly(diallyldimethylammonium chloride)] as ionic stabilizer. O2 treatment resulted in the reappearance of ligand to metal charge transfer bands of PdCl 4 2− . Repeated oxidation and hydrogen treatments caused aggregation/agglomeration of the Pd particles yielding big spherical aggregates of 30–50 nm but still keeping the size of the 5–6 nm primary particles. Aggregation was attributed to the reduction of PdCl 4 2− anion having high local densities around Pd particles surrounded by PDDA polycation. Au–Pd bimetallic hydrosols were synthesized by reduction with 2-propanol and by pulse radiolysis technique in the presence of PDDA. Both reduction modes synthesize Au core–Pd shell structures. The mode of reduction was observed to affect the particle size and the thickness of the Au core and Pd shell. At the Au rich samples the differences in the optical spectra were attributed to different dispersions of the Au–Pd particles. Au–Pd bimetallic hydrosols were adsorbed on Aerosil 200 and the supported samples were tested in gas phase hydrogenation of acetylene.

Au-TiO(2) interface on silica support was aimed to be produced in a controlled way by use of Au hydrosol. In method A, the Au colloids were modified by hydrolysis of the water-soluble Ti(IV) bis(ammoniumlactato)dihydroxide (TALH) precursor and then adsorbed on Aerosil SiO(2) surface. In method B, Au sol was first deposited onto the SiO(2) surface and then TALH was adsorbed on it. Regular and high-resolution transmission electron microscopy (TEM and HRTEM) and energy dispersive spectrometry (EDS) analysis allowed us to conclude that, in method A, gold particles were able to retain the precursor of TiO(2) at 1.5 wt % TiO(2) loading, but at 4 wt % TiO(2) content the promoter oxide appeared over the silica surface as well. With method B, titania was detected on silica at each TiO(2) concentration. In Au-TiO(2)/SiO(2) samples, the stability of Au particles against sintering was much higher than in Au/TiO(2). The formation of an active Au-TiO(2) perimeter was proven by the greatly increased CO oxidation activity compared to that of the reference Au/SiO(2).

As case studies, two methods on the preparation of supported metal nanoparticles for catalytic purposes are discussed: (i) starting from metal carbonyl clusters and (ii) growing particles in liquid phase followed by deposition on support or in situ fabricating them on the support in solid/liquid interfacial layer. We highlight the advantages and disadvantages of the different techniques with special regard to the size control and stability of the catalysts obtained.

Pd particles were prepared from PdCl 2 solution (>10 −3 M) in the presence of methanol, ethanol or 2-propanol using 60 Co radiation source to generate solvated electrons and organic reducing radicals. Temperature programmed oxidation (TPO), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been used to characterize Pd particles. Radiolytic and thermal reduction of Pd 2+ appears to take place simultaneously resulting in the extensive poisoning of Pd sites as confirmed by TPO. The relatively high intensity of the C 1s spectra at 287–290 eV binding energy (BE) confirms the presence of keto and carboxylic groups on the surface. Faceted particles decorated with smaller ones have been observed by TEM measurements. Hydrogenation of 1-octyne in n -heptane has been used as a test reaction to characterize the surface sites. The increasing hydrogenation activity in repeated experiments can tentatively be explained by partial removal of surface impurities and by disintegration some of the adhered particles upon the corrosive action of 1-octyne.

Hydrogenation of ethylene, propene (Pr), 1-butene (1B), acetylene and 1,3-butadiene (BD) was investigated over 1.74 wt.% Ag/SiO 2 and 0.67 wt.% Ag/TiO 2 catalysts in temperature range between 333 and 423 K. The catalysts were prepared by wetting SiO 2 with aqueous solution of AgNO 3 and by adsorption of silver ions on TiO 2 . After O 2 and H 2 treatments the catalysts hydrogenated ethene from about 313–323 K in a pulse microreactor system. Hydrogenation of acetylene, propene, 1,3-butadiene and 1-butene was tested in a recirculation batch reactor at 323–383 K. Acetylene hydrogenation gave mainly ethene accompanied with only limited formation of oligomers (C4+). Hydrogenation of 1,3-butadiene yielded mostly 1-butene and the cis / trans ratio in the 2-butenes was observed between 2 and 5 on Ag/SiO 2 . In competitive hydrogenation of butadiene and propene mixtures 1,3-butadiene could not entirely suppress hydrogenation of propene.

Pd/SiO2 catalysts were prepared by adsorption of Pd sols on support Aerosil 200 and characterized by transmission electron microscopy (TEM), CO chemisorption and temperature programmed oxidation (TPO). The Pd hydrosols were generated from PdCl2 solution and ethanol as reducing agent in the presence of poly(diallyldimethylammonium chloride), PDDA. The pH of the solution was increased to ensure adsorption of the Pd sol with high concentration of PDDA. The catalytic activity was tested in benzene hydrogenation. The presence of organic impurities and the role of morphology affecting the activity have been discussed in terms of the preparation procedure applied.

Silica-supported Pd catalysts were prepared at 298–353 K from Pd(II) chloride or Pd(II) acetate in suspension of SiO2 and ethanol-water or ethanol-toluene mixtures, respectively. Reduction of Pd ions diffusing from liquid phase was ensured in an ethanol-rich adsorption layer covering the SiO2 particles. Temperature-programmed oxidation (TPO) measurements were performed to characterize the organic impurities retained by solid phase. Vapour phase reduction/adsorption experiments with ethanol confirmed that under the reported reduction conditions, the Pd nanoparticles decompose ethanol and the CO formed remains chemisorbed on the Pd sites. Upon contacting the samples with air during the drying process to eliminate the solvent, the CO molecules are immediately removed from Pd sites by O2, and thereby, a significant fraction (22–34%) of Pd sites becomes accessible for catalytic reactions.

Acetylene hydrogenation and formation of surface deposits have been investigated on two series of Pd and Pd-Au/SiO2 catalysts differing in metal particle size (D=0.47 and 0.08). Gold was deposited via ionization of pre-adsorbed hydrogen over pre-reduced Pd/SiO2 in order to ensure selective poisoning of the Pd surface. The non-steady-state regime of operation and the accumulation of hydrocarbonaceous overlayer were tested in pulse-flow experiments. Concentration of surface hydrocarbonaceous deposits accumulated during different treatments was also determined by temperature programmed oxidation (TPO). Hydrocarbon overlayer was observed to form immediately and its presence appeared to be a necessary requisite to get steady-state conversion and selectivity data. A large excess of hydrogen suppressed the formation of carbonaceous laydown and increased the over-hydrogenation of acetylene. Presence of Au decreased the carbon coverage and improved the ethene selectivity. Decoration of Pd by Au and the morphology of particles explain the ethene selectivity improvement.

A Pt-Sn/γ-Al 2 O 3 bifunctional catalyst was modified by tin, bismuth and tellurium using metal adsorption technique. The parent and the modified catalysts were tested in n -octane reforming under conditions similar to industrial applications. The added tin decreased the reformate yield a little, the aromatic content decreased and the isoparaffin content increased, the research octane number remained high. Tellurium and bismuth deposited greatly deactivated the metal function of the catalyst; the liquid yield of the product is far less than that over the parent platinum–tin catalyst. The isoparaffin and aromatic selectivity however changed favourably. More isoparaffin hydrocarbon was found in the liquid product over the modified catalysts. The reforming function of the metal was suppressed and, therefore, the reactions of alkenes occurring on the acid sites of the catalyst became dominant.

Results of the last decade with respect to the selective hydrogenation of hydrocarbons with multiple unsaturation (dienes and alkynes) over heterogeneous palladium catalysts are reviewed. Factors such as metal dispersion, carbon deposits, and the use of promoters and additives controlling catalytic activities and chemo-, regio- and stereo-selectivity are discussed. A detailed treatment of the status of the selective removal of hydrocarbon impurities with multiple unsaturation from industrial feedstocks is also given.

Pd nanoparticles were prepared by ‘controlled colloidal synthesis’ (CCS) using aerosil silica support. On SiO 2 , 1–2 nm thick ethanol-rich adsorption layer in ethanol–toluene and ethanol–water mixtures was formed into which Pd(II) ions diffused and were reduced there by ethanol. Using Pd(II)-acetate precursor in an ethanol–toluene mixture (sample G1) and PdCl 2 precursor in an ethanol–water mixture (sample G2), palladium particles of 7.0 and 8.8 nm size, respectively, were produced. Effects of treatments in air and hydrogen were studied on the Pd/SiO 2 samples. The Pd particles showed a twofold/threefold increase in the catalytic activity in benzene hydrogenation after treatment in air at 573 K. The activity increase cannot be explained by a change in the particle size as indicated by transmission electron microscopy (TEM) and CO chemisorption data. Augmentation of turnover number is interpreted by the removal of carbonaceous residues and by the restructuring of the surface caused by carbon removal followed by PdO/Pd transition in the subsequent hydrogen treatment.

Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/α-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

Using different reduction conditions Pd powders have been prepared and characterized by chemisorption and TPO (Temperature Programmed Oxidation) measurements. The amount of carbon deposits introduced during preparation seems to be peculiar to the preparation procedure. The O2 consumption curves attributed to PdO formation have shown two peak minima suggesting strong differences in the accessibility of Pd particles.

Formation of carbonaceous deposits from 1,3-butadiene has been investigated over a group of Pd catalysts. Hydrogen generated in decomposition of diene at 473–523 K participates in diene hydrogenation, resulting in the formation ofn-butenes. XRD measurements have confirmed formation of dissolved carbon (PdCx) phase. DRIFT measurements over 0.06 wt.%Pd/γ-Al2O3 have revealed bands at 1575 and 1464 cm−1, suggesting formation of carboxylate structures. Selectivity of the competitive hydrogenation in 1,3-butadiene and propene mixture R(BD)/R(Pr) has been measured on “fresh” and poisoned samples. Accumulation of deposits has decreased the R(BD)/R(Pr) ratio. The results have been interpreted by transport hindrance and a greater prevalence of non-selective low coordination sites on the poisoned surface. Measurements over Pd, Cu, Pt and Rh catalysts have shown that the highn-butane selectivity over Pt and Rh is also accompanied with low R(BD)/R(Pr) values, suggesting that thermodynamic and mechanistic factors are not entirely separable.

Gas phase hydrogenation of 1,3-butadiene, propene, and mixtures of 1,3-butadiene and propene has been investigated over 0.05 wt% Pd/Al 2 O 3 catalyst. The catalyst was deliberately poisoned by methane (513 K) or diene (473 K) and the effect of the hydrocarbonaceous materials was tested on the product selectivity and the rate of hydrogenation of diene–propene mixtures. It has been concluded that a large quantity of hydrocarbonaceous deposit decreases the surface fugacity of diene due to transport hinderance and in consequence enhances the over-hydrogenation of diene and permits the hydrogenation of propene in the presence of diene.

Gas phase semi-hydrogenation of 1,3-butadiene has been investigated over Pd catalysts of egg-shell type containing 0.03–0.05 wt% Pd. The measurements concentrated on the effect of the hydrocarbonaceous deposits formed from methane or butadiene at 473–523 K. The carbonaceous material has influenced the over-hydrogenation selectivity ( n -butane formation) and the distribution of n -butenes. Under the reported conditions the deposits form three-dimensional islands and in the case of diene they are also present on the support sites. The poisoning experiments with Pd-powder confirmed the formation of PdC x phase from both methane and butadiene. Deliberate diene and prolonged methane poisoning at 513 K (18 h) increased the n -butane selectivity and decreased the 1-butene/2-butene and trans -/ cis -2-butene ratios with simultaneous decrease of the apparent activation energy of hydrogenation. The results are interpreted by transport hinderance which affects mainly the surface fugacity of diene.

Pd—Ag catalysts poisoned by trapped hydrocarbons have been tested for selective hydrogenation of 1,3-butadiene (BD) at 284 K in a static recirculation reactor. Two levels of carbon poisoning were investigated: (i) the effect of self-poisoning (aging) in successive experiments at 284 K and (ii) the effect of deliberate poisoning. In the latter case first butadiene or acetylene was circulated over the catalyst above 373 K and then the activity and the selectivity of BD hydrogenation was tested over the poisoned surface at 284 K. The successive experiments performed at 284 K in H2/BD=2.2 mixtures resulted in the severe poisoning of the reaction sites. The steady state activity of the self-poisoned samples was about 1% of the initial activity. Vacuum or O2 treatment at T < 433K of the self-poisoned samples increased the hydrogenation activity. The result has been interpreted by surface restructuring of the hydrocarbonaceous deposits which apparently brings about re-creation of certain sites. Because of hydrogen's low surface fugacity and high stability of the multiple bonded probably oligomer species hydrogen treatment at T < 473K was not sufficient to restore the original activity. The selectivity of n-butane was initially less than 0.05% at 40–55% conversions and was not affected by self-poisoning. However, as the amount of polymers built up upon deliberate poisoning at 385–488 K following diene and acetylene treatments the n-butane selectivity gradually increased. The deliberate poisoning influenced only to a small extent the consumption of butadiene while the ratio: R1−B/RBD (rate of 1-butene consumption/rate of BD consumption) decreased from 3 to 0.1. Normal isotope effect of hydrogen addition was observed over both self-poisoned and deliberately poisoned catalysts: RH/RD was found to be less for n-butane formation than for BD consumption. Formation of n-butane on the catalyst has been interpreted by slow diene transport caused by the presence of oligomer layers on metal sites.

Selective semi-hydrogenation of 1,3-butadiene has been investigated in excess of hydrogen over Co, Cu and Pd—Ni catalysts. The results on 5 wt.-% Co/Al2O3 and Pd—Ni/Nb2O5 catalysts provide evidence that hydrocarbonaceous materials formed on these surfaces play an important role in governing the competition between 1,3-butadiene and n-butenes. Similar results have been observed on 5 wt.-% Cu/SiO2 modified by preadsorption of n-butylamine. On the poisoned surface hydrogenation and isomerization of n-butenes have been remarkably inhibited, but the sample remains active in semi-hydrogenation of 1,3-butadiene. It is proposed that the unusual high selectivity of alkene formation is ensured by firmly held adspecies (FHA) formed from diene or n-butylamine. FHA cover and modify metal sites and do not allow adsorption of n-butenes as they apparently cannot compete with FHA. Hydrogenation of diene has been interpreted by a compression-displacement model, in which the high strength of diene complexation plays a definite role. Butadiene ‘pushes away’ FHA for reason of its high complexation strength and finds (create) reaction sites for its semi-hydrogenation. Preadsorption of CH3OH on 5 wt.-% Cu/SiO2 affects the regionselectivity of n-butenes: on the modified surface the selectivity of cis-2-butene increases at the expense of 1-butene. These results have been interpreted by electronic modification of Cu sites by intermediates formed from decomposition of methoxy species.

The effect of acidic sites on activity and product selectivity has been investigated in 1,3-butadiene hydrogenation over platinum catalysts prepared with high purity Al2O3 supports (Condea SB, Woelm N, Degussa Alumina C, ICN-N). Degassing the reduced samples at 723 K has increased the selectivity of n-butane formation on catalysts of high platinum dispersion (DCO=68–93%). Over Woelm and ICN aluminas isomerization of 1-butene formed on platinum sites to cis- and trans-2-butene can also be observed. Poisoning the catalysts with water, ammonia and ethylenediamine (EDA) suppresses isomerization of 1-butene, but only EDA hinders markedly formation of n-butane. The results have been interpreted by participation of Lewis acid sites and by contribution of electron deficient platinum sites in the vicinity of the metal-support interface.

Hydrogenation of 1,3-butadiene was investigated on catalysts prepared from an amorphous ribbon of composition Pd2Ni50Nb48, activated by oxygen and hydrogen treatments at 683 K. The hydrogenation activity of the sample decreased gradually with time, indicating formation of carbonaceous materials (oligomers). As a consequence of oligomer formation the butene selectivity remained constant even at 100% butadiene conversion. Apparently n-butenes could not compete with oligomers. Restart experiments confirmed that diene, due to its high strength of complexation, is able to adsorb on metallic sites in the presence of oligomers. The results emphasize the role of oligomers in selective semihydrogenations.

The selective hydrogenation of 1, 3-butadiene was studied in the presence of a 10:1 excess of 1-butene over supported bimetallic catalysts containing palladium in a vapour phase atmospheric plug flow reactor in the temperature range 288–313 K. Addition of copper to alumina-supported Pd increases its selectivity for converting butadiene to n-butenes without saturating or isomerizing the n-butenes. For example, with atomic ratio Cu/Pd = 2, the bimetallic catalyst selectively converts > 99% of the diene to n-butenes while isomerizing or saturating less than 1% of the starting 1-butene. Under similar conditions, Pd alone maintains high n-butene selectivity to only about 50% conversion of the diene. Over both catalysts the kinetics of 1, 3-butadiene hydrogenation are first order in hydrogen and zero order in butadiene. Hydrogen sorption experiments showed that Cu addition decreases both the surface adsorption and the bulk absorption, the former suggesting surface decoration of Pd by Cu and the latter indicating significant bulk Cu-Pd interaction in the supported bimetallic samples.

The formation of Au/TiO 2 nanostructured interface on SiO 2 support using Au hydrosol and Ti-isopropoxide or Ti(IV)-bis(ammonium lactato) dihydroxide (TALH) precursors has been investigated in context of preparing a novel type of catalysts active in the CO oxidation. Different preparation routes were compared: (i) Au sol was modified by Ti-precursor then adsorbed on silica followed by calcination, (ii) Au/silica was modified by Ti-precursor and calcined, (iii) Au was deposited on SiO 2 modified by Ti-precursor and calcined. The enhanced catalytic activity in the CO oxidation compared to that of the analogue anatase supported Au catalyst is possibly due to several factors, such as, the morphology of TiO 2 (likely amorphous) and formation of Ti-O-Si interaction, which results in the formation of large and efficient interface between Au and TiO 2 . This was supported by examination of the mechanical mixtures of SiO 2 and anatase supported Au catalysts as well as their modified alternatives.

Palladium nanoparticles have been fabricated on Aerosil 200 support using (i) “Controlled Colloidal Synthesis”, (ii) PDDA stabilized Pd sol (both liquid phase reduction with ethanol) and (iii) incipient wetness method (as reference) Oxidation/reduction treatment was employed to remove the carbonaceous impurities from the samples during which no change in the particle size was experienced. However, the turnover frequency referred to Pd surface exposed significantly changed and FTIR technique was used to monitor the alteration of Pd surface by means of CO chemisorption It turned out that after treatment the distribution of the overlapping stretching band system of the prevailing bridge CO forms was changed indicating either a change in the face orientation of Pd crystallites, or formation of clean Pd faces in oxidation/reduction process

Catalytic behaviour of Pd 2 Ni 50 Nb 48 amorphous ribbon and Pd-Ni/SiO 2 catalysts has been investigated in hydrogenation of 1,3-butadiene. Pd-Ni/SiO 2 catalysts were prepared using vapor phase adsorption and decompostion, of Pd(acac) 2 over Ni/SiO 2 and Ni(CO) 4 over Pd/SiO 2 . Presence of Ni has been observed to increase the selectivity of competitive hydrogenation of 1,3-butadiene in propene or 1-butene. The high selectivity of Pd-Ni in competitive hydrogenation has been interpreted by geometric effects caused by dilution of Pd with Ni and and partial poisoning of Pd-Ni ensembles by firmly held adspecies.

Effects of hydrocarbonaceous deposits have been investigated in hydrogenation of 1,3-butadiene over Pd-Ag/Al2O3 catalysts. Studies on the effect of various treatments on self-poisoned samples revealed very different behavior of the surface deposits. Because of hydrogen's low surface fugacity, hydrogen treatment was not sufficient to remove surface species at T

The effect of the support in constraining the formation and defining the structure of bimetallic particles has been considered. Alumina and NaY zeolite supported platinum and cobalt bimetallic catalysts are illustrated to rationalize this effect. The surface composition and dispersion of the bimetallic particles are further correlated with the catalytic activity of bimetallic catalysts in CO hydrogenation.

Several catalysts with 1 w% Pd + x w% Ag (x=0, 0.1, 1, 2) have been supported on αAl 2 O 3 or Na modified Na-Al 2 O 3 , and tested for the selective hydrogenation of 1,3-butadiene (BD) in the presence of 1-butene (1-B). With all catalysts the activity decreases markedly with aging due to accumulation of carbonaceous residue on the surface. Alloying the Pd with Ag and neutralising the acid sites on the support with Na both have significant effects on the selectivity, i.e. converting BD directly to n-butenes without isomerizing or hydrogenating significant quantities of the 1-butene. Addition of Ag to the Pd decreases the hydrogenation activity but increases the selectivity for BD conversion to butenes, although solid state and chemisorption measurements indicated that mixing of the two metals is limited under these conditions. Experiments with 13 C-BD demonstrated that the major reaction pathway is to 1-B (〉50%). When normalized to the same pressure, much more of the product n-butane is formed from the BD than from 1-B. Alternate exposure to 13 C-labeled and unlabeled BD showed that the surface residue does not mix significantly with the reactants and is formed predominantly from the BD, not the n-butenes. The presence of Na in the support seems to inhibit Pd/Ag mixing and results in decreased selectivity; some of the Pd or Ag may be encapsulated in the Na 2 O.

The irreversible adsorption and coke formation from methane, n-hexane, 1-hexene and 1,5-hexadiene were investigated on Pt/Al2O3 and Pt-Sn/Al2O3 between and 450°C. Depending on temperature, chemisorption, coke precursor and coke formation have been observed. Coke precursors are formed on Pt sites and transferred to alumina. Two routes of coking were observed. Presence of tin decreases the adsorption bond strength of 1-hexene and at low concentrations increases the amount chemisorbed. This phenomenon is explained by the ensemble effect. A drain-off effect is proposed to explain the decrease of the coke coverage on the metallic sites upon addition of Sn.

Homologation of n-pentane and cyclopentane results in formation of benzene on Ru, Os, Re and Ir/SiO2 catalysts. Formation of benzene can be explained by the insertion of carbene into terminal vinilic carbon followed by C6-dehydrocyclization.

The effect of dispersity of Ni catalysts has been investigated in the hydrogenolysis of ethane. The kinetic order in hydrogen and the apparent activation energy are dependent on the dispersity. The experimental results reveal that the structure sensitivity of this reaction appears to a certain extent through the variation of the hydrogen order.

Adsorption of cyclohexanol on Pt SiO 2 catalyst was investigated by means of ir spectroscopy. At room temperature hydrogen atoms from both OH and tertiary carbons split off easily, resulting in the formation of cyclohexanone held on SiO 2 by hydrogen bonds whereas on Pt it is held by a π-bond or through the lone electron pair of oxygen. Dissociation of α-hydrogens in cyclohexanone commences only at circa 353 K. At 393 K bands characteristic of an enolic system were observed, suggesting formation of a π-oxoallylic species during dehydrogenation of cyclohexanone.

The composition and deactivation effect of green oil on a Pd/A1203 catalyst (ICI 38-1) in the hydrogenation of a tail-end acetylene-ethylene mixture are discussed. Infrared and NMR measurements confirmed the presence of carboxylic acids in the oil. The green oil poisoned the acetylene hydrogenation sites but the product distribution pattern was not greatly affected.

The self-poisoning effect of deuterium exchange reactions of C1−C6 straight chain aliphatic hydrocarbons as well as hydrogenolysis and dehydrocyclization of n-hexane in the presence of deuterium on a nickel powder catalyst has been investigated. The poisoning is enhanced with increasing carbon number. The results can be correlated to the ease of dissociative adsorption, i. e. to the formation of multiply bonded species. A tentative model is proposed to explain the “decrease” of deuterium exchange in n-hexane when the reaction is shifted towards hydrogenolysis and benzene formation. It is shown that at elevated temperatures the poisoning upon deuterium exchange is caused not only by blocking of the active sites with deposits but also by hindrance of desorption of the starting molecules in the original/exchanged form.

The reaction of 2-methylpropane has been investigated in presence of helium and hydrogen over a platinum black catalyst. The appearence of olefins in the gas phase indicates that the precursor of these unsaturated compounds adsorb ed on the surface may have some role in the self-poisoning observed during hydrogenolysis and/or isomerization.

Transformation of n-hexane has been investigated as a function of partial pressure of hydrogen at 563K over Pt catalysts including Euro-Pt-1. The carbon coverage and the fraction of free sites on the working catalysts together with product distributions have been determined. The conclusions are as follows: (1) The partial pressure of hydrogen regulates the coverage of the firmly held hydrocarbons which in turn for geometric/electronic reasons affect the product selectivity; (2) Independently of the size of the Pt particles, with the increase of the partial pressure of H 2 , the only reaction whose selectivity has been observed to increase continuously is fragmentation. Extrapolation of the selectivity values to large excess of H 2 seems to indicate that the structure sensitivity of the product selectivity ceases at large H 2 /nH ratios.

The effect of aging on the hydrogenation of a tail-end mixture (0.29 mol % C2H2, 0.44 mol % H2 balanced by C2H4) has been investigated on Pd-black and on various Pd/Al2O3 catalysts. Over supported catalysts the selectivity of ethylene formation decreases with time on stream in the first 40–60 hours of operation whereas the C2H2 conversion is not, or only slightly, influenced. With Pd-black the selectivity of ethylene formation changes in the opposite direction.14C-C2H2 experiments have revealed that the aging has only a minute effect on the intrinsic selectivity of C2H2 hydrogenation. The effect of the surface polymer and the nature of the ethylene hydrogenating sites are discussed. The results with supported catalysts have been interpreted by a polymer promoted hydrogen spillover.

The mechanisms of aromatization of C 6 and C 7 alkanes have been investigated over Ni catalysts. On the basis of radioactive measurements with [3- 14 C]methylpentane it was concluded that benzene is formed both by a CH x addition—abstraction mechanism and by intramolecular rearrangements. A change of the product selectivity with hydrogen pressure has been interpreted in terms of a change in the ensemble size of Ni governed by strongly adsorbed hydrocarbon fragments.

The mechanism of dehydrocyclization has been investigated with a group of branched C6 and C7 isomeric hydrocarbons containing only four or five carbon atoms in the main chain on Ni and Co catalysts of small and medium dispersion in the temperature range 573–650 K. At low H2HC ratios transformation of 2-methylpentane, 3-methylpentane, and 3-ethylpentane yields toluene and ethylbenzene, respectively, besides benzene. Evidence is presented that the formation of benzene takes place via CHx-addition to a vinylic group, 1,6-ring closure, and CHx-abstraction in the adsorbed phase. In the proposed reaction sequence the rate of CHx insertion is regarded as the rate-limiting step of aromatization. Participation of the bond-shift or the C5-cyclization route of aromatization is not significant over Ni and Co.

Data on chemisorption of ethane on transition metal blacks have been correlated with hydrogenolysis activity measurements. On Pt and Pd the rupture of the C−C bond seems to be a hindered process. Desorption of methane requires larger activation on Co and Ni than on Ru, Rh or or Ir blacks.

The skeletal rearrangement reactions of butane, 2-methylpropane and 2,2-dimethylpropane were investigated over Al2O3- and SiO2-supported Pd, Pt, Ni and AgNi catalysts. As opposed to Pt, isomerization over the other catalysts proceeds mainly by carbene intermediates by a so-called “external C1-migration” pathway. This reaction is parallel with homologation. Hydrogen sensitivities and radiotracer studies confirm these suggestions.

The hydrogen sorption of carbon-supported platinum catalysts, studied by the potentiodynamic method, differs significantly from that of unsupported platinum. The difference depends on the preparation method and on the nature of the support. Possible explanations are suggested as (i) some kind of interaction between metal and support atoms during impregnation, (ii) high dispersity (amorphous structure) and (iii) hydrogen spillover onto the carbon support.