Catalysis of Organic..

Nikoshvili et al . 181gasometrical burette. Before the test the catalysts were saturated with hydrogen. Bothsaturation and catalytic experiments were conducted at atmospheric pressure.Duration of the saturation was 1h. Samples (from 5 to 9 in each test) were takendepending on the hydrogen consumption. Most of the samples were collected in thebeginning of the experiment (until the half of the hydrogen amount is consumed).The influence of various solvents (water, methanol, ethanol, propanol, isopropylalcohol (i-PrOH) and toluene) on the catalysts behaviour to provide the appropriateswelling of the above-mentioned polymeric matrixes and layers, their stability andcatalytic activity during the experiments was investigated. PS-b-P4VP is soluble inorganic solvents (e.g. toluene), while metal salt is not. So, the latter is solubilizedsolely in the micelle core due to interaction with pyridine units (15). In the case ofwater-soluble PEO-b-P2VP the probability of the existence of metal salts outside ofthe micelle cores is higher. Thus for Pd-PEO-b-P2VP and Pd-PEO-b-P2VP/Al 2 O 3catalysts, a 7:3 (vol.) ratio of isopropyl alcohol to water was found to be optimal(16).Kinetic studies were performed at various of substrate-to-catalyst ratios andtemperature. Physical-chemical investigations of the catalysts, substrate and productwere conducted via gas chromatography (GC Chrom-5 equipped with FID), IR-, XPandelectron-spectroscopy. In order to find micelle characteristics providing a kineticregime, TEM and AFM studies were performed. Micelle sizes in solutions wereexamined by spectra turbidity method using photoelectrical colorimeter FEK-56M(Russia) equipped with the high-pressure mercury–quartz lamp (DPK-120). Thehypotheses of hydrogenation mechanisms were offered on the basis of the results ofkinetic experiments, physical-chemical investigations and mathematical modeling.Results and DiscussionFor all investigated catalysts the optimal conditions (see Table 1) of thehydrogenation were found.It can be seen from the Table 1 that in the case of Pd-PS-b-P4VP and Pd-HPScatalysts the optimal temperature is higher (90°С). The higher temperature of thereaction (which does not allow destructing the polymeric matrix) led to the higherselectivity due to the increase of the active sites accesibility because of the betterswelling of the polymer.Table 1. Optimal conditionsCatalystPd-PEO-b-P2VPTemperature,o CC c a , molPd/lC o b ,mol/lSolvent70 1.8⋅10 -5 0.44 i-PrOH +waterIntensity ofshaking,shaking/min960