Pt behavior in the Pt-C-S ± Fe-HO system at 200-400°C and P = 1 kbar: Experimental results.

The effect of sulfur on platinum adsorption on carbonaceous matter (CM) was experimentally studied at 200-400°C and P = 1 kbar. The IR spectra of the experimental products indicate that sulfur accelerates HC condensation and aromatization, but the effect of sulfur on platinum concentrations in the organic fractions is within the analytical uncertainties. SEM images show the development of a multilayer porous carbonaceous film on the walls of the ampoules and platinum in physical contact with carbonaceous matter. The composition of the film varies, depending on its thickness (3-25 μm), within the following limits: 61.06-100 wt % C, 0-33.7 wt % Pt, 0-5.17 wt % O, and 0-0.74 wt % S. The film contains tiny Pt crystals, whose morphology varies with increasing duration of the experiments from nanometer- and micrometer-sized spheroids to subequant, tabular, and wire-like. Depending on their size, the composition of the crystals varies as follows: 23.30-52.45 wt % Pt, 49.57-73.52 wt % C, and 0-4.20 wt % O. According to our SEM data, the kerogen also contains tiny crystalline segregations of carbon aceous platinum whose morphology and composition are analogous to those on the film. The presence of carbon in the tiny platinum crystals deposited from solution can be explained by the background effect of the kerogen of the film and/or by their crystallization from organo-platinum complexes. In our kinetic experiments, local electrochemical reactions produced aggregates of nanometer-sized (60-250 nm) spheroids around larger micrometer-sized (up to 10 μm) spheroids, whose aggregation resulted in larger crystals and their further transformation. The polymorphism, hierarchical aggregation, and compositional variability of the platinum segregations are likely typical of car- bon-bearing systems because of their crystallization from metastable organo-platinum complexes. [ABSTRACT FROM AUTHOR]