Sensitivity of CO oxidation toward metal oxidation state in ceria-supported catalysts: an operando DRIFTS-MS study

The oxidation of carbon monoxide has been studied on pristine CeO2, Rh–CeO2, and Pt–CeO2 powders prepared in one step by solution combustion synthesis (SCS). The reaction was cycled between an oxygen-rich and a CO-rich feed with regard to the stoichiometric conditions. CO2 production was monitored by mass spectrometry, while the surface species were probed by operando DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy). Whereas the reaction starts above 150 °C on CeO2 and Rh–CeO2 and does not depend on the state of the surface (oxidized or reduced), the reaction on Pt–CeO2 shows strong dependency on the initial state and substantial activity is achieved at much lower temperatures with the CO-rich feed. We relate this result to the change in the oxidation state of Pt via strong interaction with ceria

Porphyrin Metalation at the MgO Nanocube/Toluene Interface

Molecular insights into porphyrin adsorption on nanostructured metal oxide surfaces and associated ion exchange reactions are key to the development of functional hybrids for energy conversion, sensing, and light emission devices. Here we investigated the adsorption of tetraphenyl-porphyrin (2HTPP) from toluene solution on two types of MgO powder. We compare MgO nanocubes with an average size <i>d</i> < 10 nm and MgO cubes with 10 nm ≤ <i>d</i> ≤ 1000 nm. Using molecular spectroscopy techniques such as UV/vis transmission and diffuse reflectance (DR), photoluminescence (PL), and diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy in combination with structural characterization techniques (powder X-ray diffraction and transmission electron microscopy, TEM), we identified a new room temperature metalation reaction that converts 2HTPP into magnesium tetraphenyl-porphyrin (MgTPP). Mg²⁺ uptake from the MgO nanocube surfaces and the concomitant protonation of the oxide surface level off at a concentration that corresponds to roughly one monolayer equivalent adsorbed on the MgO nanocubes. Larger MgO cubes, in contrast, show suppressed exchange, and only traces of MgTPP can be detected by photoluminescence

Insights in Reaction Mechanistics: Isotopic Exchange during the Metalation of Deuterated Tetraphenyl-21,23<i>D</i>‑porphyrin on Cu(111)

Through the use of temperature-programmed desorption (TPD), the self-metalation and dehydrogenation of deuterated 5,10,15,20-tetraphenyl-21,23<i>D</i>-porphyrin on Cu(111) have been studied, resulting in new insight into the metalation of porphyrins on surfaces. The metalation is found to proceed through the transfer of the central aminic hydrogen atoms to the Cu(111) surface and not, as suggested by gas phase calculations, through the combination of the hydrogen atoms to molecular hydrogen above the partially inserted metal center. This finding suggests that the metalation reaction could be significantly influenced by the stability of hydrogen on the substrate surface. The metalation reaction and the subsequent hydrogenation and dehydrogenation of the periphery of the porphyrin molecule leading to hydrogen–deuterium exchange are modeled with a simple microkinetic reaction model. The model is able to describe the main features of the TPD spectra