Structural determination by XAFS spectroscopy of non-porphyrin nickel and vanadium in maya residuum, hydrocracked residuum, and toluene-insoluble solid

The local structure of non-porphyrin Ni and V in Maya residuum, hydrocracke d residuum, and toluene-insoluble solid were determined by XAFS spectroscop y. In residuum, the first coordination shell of non-porphyrin V is similar to that for vanadyl tetraphenylporphyrin with four N at a distance of 2.08 Angstrom and one O at 1.67 Angstrom. Similarly, the first coordination shel l of Ni non-porphyrin is similar to that in nickle tetraphenylporphyrin, i. e., four N at a distance of 1.90 ii. The Ni and V coordination geometries a re remarkably stable toward thermal cracking, catalytic hydrogen, and H2S. After hydrocracking to about 60% conversion of the residuum, the local coor dination of Ni and V in the hydrocracked residuum is little changed. During hydrocracking, approximately 1% of the residuum is converted to toluene-in soluble solid, which contains high levels of Ni and V. Approximately 10% of the Ni and V in the solid is still present in a porphyrin-type coordinatio n geometry, while the remaining Ni and V has an octahedral coordination. In the latter, the V coordination contained one O at 1.64 Angstrom, four N at 2.14 Angstrom, and one N (or O) at 1.96 Angstrom, and the Ni coordination contained six N at 2.09 Angstrom. Ni or V sulfides are not formed in the to luene-insoluble solid.