Direct catalytic methane functionalization, a "dream reaction", is typically characterized by relatively low catalyst activities. This also holds for the η(2)-(2,2'-bipyrimidyl)dichloroplatinum(II) [(bpym)PtCl2, 1] catalyst which oxidizes methane to methyl bisulfate in sulfuric acid. Nevertheless, it is arguably still one of the best systems for the partial oxidation of methane reported so far. Detailed studies of the dependence of activity on the SO3 concentration and the interplay with the solubility of different platinum compounds revealed potassium tetrachloroplatinate (K2PtCl4) as an extremely active, selective, and stable catalyst, reaching turnover frequencies (TOFs) of more than 25,000 h(-1) in 20% oleum with selectivities above 98%. The TOFs are more than 3 orders of magnitude higher compared to the original report on (bpym)PtCl2 and easily reach or exceed those realized in commercial industrial processes, such as the Cativa process for the carbonylation of methanol. Also space-time-yields are on the order of large-scale commercialized processes.

Platinum and platinum alloys supported on carbon materials are the state of the art electrocatalysts for the essential oxygen reduction reaction (ORR) in low-temperature fuel cells. The limited stability of such materials under the often detrimental operation conditions of fuel cells still remains a critical issue to improve. In this work, we explore the impact of nitrogen-doped carbon supports on the activity and stability of platinum-based fuel cell catalysts. We present a nitrogen-doped mesostructured carbon material, nitrogen-doped hollow carbon spheres (NHCS), as a support for platinum-based electrocatalysts. A detailed study of the electrochemical activity and stability was carried out for two Pt@NHCS materials i.e., as-made material (Pt@NHCS) with a Pt particle size smaller than 2 nm and the corresponding material after thermal treatment at 850 degrees C (Pt@NHCS_ΔT) with a Pt particle size of ca. 23 nm. Activity in the ORR was studied by rotating disc electrode (RDE) thin-film measurements, and electrocatalyst stability was evaluated by accelerated aging tests under simulated startstop conditions. The performance of the NHCS-based materials was compared to the two corresponding nitrogen-free materials as well as to a standard Pt/Vulcan catalyst. The underlying degradation mechanisms of Pt@NHCS materials were investigated via identical location electron microscopy. Our results conclusively show that nitrogen doping of the carbon supports can offer benefits for achieving high initial mass activities due to improved high platinum dispersion; however, it was not found to necessarily lead to an improvement of the catalyst stability

Combining advantages of homogeneous and heterogeneous catalysis by incorporating active species on a solid support is often an effective strategy for improving overall catalyst performance, although the influences of the support are generally challenging to establish, especially at a molecular level. Here, we report the local compositions, and structures of platinum species incorporated into covalent triazine framework (Pt-CTF) materials, a solid analogue of the molecular Periana catalyst, Pt(bpym)Cl₂, both of which are active for the selective oxidation of methane in the presence of concentrated sulfuric acid. By using a combination of solid-state 195Pt nuclear magnetic resonance (NMR) spectroscopy, aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), important similarities and differences are observed between the Pt-CTF and Periana catalysts, which are likely related to their respective macroscopic reaction properties. In particular, wide-line solid-state 195Pt NMR spectra enable direct measurement, identification, and quantification of distinct platinum species in as-synthesized and used Pt-CTF catalysts. The results indicate that locally ordered and disordered Pt sites are present in as-synthesized Pt-CTF, with the former being similar to one of the two crystallographically distinct Pt sites in crystalline Pt(bpym)Cl₂. A distribution of relatively disordered Pt moieties is also present in the used catalyst, among which are the principal active sites. Similarly XAS shows good agreement between the measured data of Pt-CTF and a theoretical model based on Pt(bpym)Cl₂. Analyses of the absorption spectra of Pt-CTF used for methane oxidation suggests ligand exchange, as predicted for the molecular catalyst. XPS analyses of Pt(bpym)Cl₂, Pt-CTF, as well as the unmodified ligands, further corroborate platinum coordination by pyridinic N atoms. Aberration-corrected high-angle annular dark-field STEM proves that Pt atoms are distributed within Pt-CTF before and after catalysis. The overall results establish the close similarities of Pt-CTF and the molecular Periana catalyst Pt(bpym)Cl₂, along with differences that account for their respective properties