Controlling Selective C–O and C–H Bond Scission of Methanol by Supporting Pt on TiN and Mo ₂ N Model Surfaces and Powder Catalysts

Transition metal nitrides (TMNs) have been explored as effective supports for Pt due to their Pt-like electronic properties. However, there is a lack of fundamental understanding regarding the behavior of Pt on different TMNs (Pt/TMN). Herein two TMNs, Mo2N and TiN, were modified with Pt and compared using methanol decomposition as a probe reaction via both ultrahigh vacuum (UHV) studies on thin films and ambient-pressure batch reactor studies of powder catalysts. Temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) measurements were conducted under UHV conditions with Mo2N and TiN thin films. Mo2N was shown to favor C–H bond scission to form CO with a 56.2% selectivity, while TiN favored C–O bond scission to form CH4 with a 74.5% selectivity. The addition of 0.9 monolayers (MLs) of Pt increased C–H bond scission selectivity to 89.7% and 49.2% for Mo2N and TiN respectively. Density functional theory (DFT) calculations on model surfaces revealed that the binding energy of O (BE*O) was significantly reduced on Pt/TMNs, from −4.02 eV on Mo2N to −1.31 eV on Pt/Mo2N and −4.74 eV on TiN to −1.37 eV on Pt/TiN. As a result, C–O bond scission pathways were suppressed, leading to the preferential C–H bond scission that was observed experimentally. The C–O and C–H bond scission trends observed on thin films were then extended to powder catalysts, which demonstrated similar trends toward methanol decomposition. Results from the current study establish that by combining UHV studies and DFT calculations over model surfaces, one can effectively predict the catalytic behavior of realistic TMN powder catalysts.