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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.

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.

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.

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.

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.