III International Conference

PP-I-34that the heat effect of reaction correlates with values of apparent activation energy (p > m > o)only in a case of adsorption of nitroaromatic molecule on an edge of cluster.It is well known in organic chemistry of aromatic compounds that the replacement of themore electronegative substitute NO 2 by NН 2 should easy be carried out in a meta-position ofphenols as proves to be true in accounts of the corresponding molecules in absence of thecatalyst, at adsorption on a top and on a side of tetrahedron. Аdsorption on an edge oftetrahedron breaks alternation of heat effect of reaction.Figure 1 Cluster Pd4 with adsorbed molecules of p-, m -, o-nitro- and aminophenolsThe electron-microscopic study of the catalyst has shown that on a surface there arecrystal pieces of Pd of size 500 Å and larger pieces of PdO. In the case it is possible topropose that the quantum-chemical model of “adsorption” on tetrahedron edge in a reality cancorrespond to adsorption on «shelf» of catalyst surface.Таble 1 РМ3 calculation of total heat effect ΔΔH f , кcal/molΔHf (кcal/mol)ΔΔHf (кcal/mol)Nitrophenol Аminophenol Total heat effectp- m- о- p- m- o- p- m- o-Experimental hydrogenation rate, mmol/min.g 280 250 210Apparent activation energy, кcal/mol 6,0 6,6 7,1free -31.91 -29.77 -28.74 -23.45 -24.21 -22.06 -58.23 -61.13 -60.01moleculePd -53.97 -50.05 -57.89 -38.64 -40.35 -36.33 -51.33 -56.98 -45.12Pd 4 -top 56.68 45.46 34.56 78.09 81.75 68.65 -45.28 -30.4 -32.6Pd 4 (side) -9.63 21.85 -8.90 21.47 32.91 21.64 -35.6 -55.6 -36.2Pd 4 (edge) -54.01 -60.23 -86.35 -42.67 -34.61 -45.04 -55.35 -41.07 -25.38ΔH f (2*Н 2 О) = - 106.92 кcal/molΔH f (3*Н 2 ) = - 40.23 кcal/mol69