Symposium on Recent Advances in Heteroatom Removal Presented Before the Division of Petroleum Chemistry, Inc. 215th National Meeting, American Chemical Society Dallas, TX, March 29-April3, 1998 Linear Correlations between HDS Activity and QM Parameters M. M. Ramirez de Agudelo, Ivan Machfn and M. E. Grillo INI'EVEP S.A. Apdo. 1070A, Caracas, Venezuela Fernando Ruette and A. Sie"alta /VIC Apdo. 21827, Caracas, Venezuela INTRODUCI'ION The possibility of establishing direct correlations between microscopic and macroscopic properties of a given system might be interesting. For a family of chemical reactions, some direct correlations between kinetic con- stants with quantum parameters associated to molecules (reactants or prod- ucts) or reaction intermediates have been established (1). A quantitative correlation be- tween kinetic data and molecular (microscopic) parameters for a given reaction of industrial interest might be of particular value when optimiz- ing a catalytic system. These correla- tions have been constructed using LFER, which have also applied in het- erogeneous catalytic systems (1). In recent years, LFERs have been estab- lished for complex catalytic systems of significance for the oil refining in- dustry. These types of correlations are of economic importance in cata- lyst development, since they could reduce significantly the number of re- quired experiments. The present work is the continu- ation of a first effort to apply the LFER concept to hydrodesulfurization processes {2). The obtained trends, along the transition series, for the HDS activity of the TMS catalysts are therein described in te rms of a simple model based on the strength of met- al-sulfur bonds. Methodology Restricted Open Hartree-Fock (ROHF) cluster calculations were per- formed in order to evaluate the metal sulfide quantum properties, within the IND01 model employing the Zindo package of Molecular Simula- tions Inc. (3). Previous results, where the potentialities of the LFER applica- tion using catalyst parameters were envisioned, were obtained at the CNDO level (2). Sulfide cluster mod- els of an asymmetric unit cell in size were used. Cluster geometry as taken from the crystallographic data (4) were held rigid throughout the SCF calculations. 32 The reactivity data for the reac- tions of dibenzothiophene HDS and biphenyl hydrogenation, at530 K and atmospheric pressure, were taken from Lacroix et al. (5). The catalytic activity, for a given sulfide, is taken as the number of converted molecules x1o- 10 /sec x m 2 , similarly as defined by these authors. In the present calcu- lations, the final metal sulfide phases after the HDS process reported by Lacroix et al, were considered. The metal-sulfur Electronic Dia- tomic Energies (EDE) are calculated using an energy partitioning scheme presented by Kollmar et al. for the analysis of ab ini tio and semi-empiri- cal SCF calculations (6). The resulting value might be associated with the bond strength and has been proposed by Ruette and sanchez as a tool for bond analysis (7). Within semi-em- pirical methods, the following ex- pression is obtained: where hij, Pij and fij are the one elec- tron, bond order and Fock matrix ele- ments, as obtained from the INDOl calculations. RESULTS AND DISCUSSION Figure 1 shows the best line fit of the calculated EDE (in Hartrees) to the experimental {S/M)*Ln{HDS) (where S/M is the experimental sul - fur-metal ratio, and Ln(HDS) is the logarithm of HDS activity) for metal sulfides of the first and second row series. The fitting parameters, (ex. the correlation factor, .; = 0.96/ for both