| dc.description.abstract | We designed a near-ambient-pressure (NAP) reaction cell installed inside an ultrahigh vacuum (UHV) chamber to investigate the instantaneous dynamics of surface catalytic reactions with the coupled femtosecond-resolved ultra-broadband IR spectroscopy. The reaction cell is installed in this way, because the samples, catalytic model systems, are prepared under UHV conditions to prevent contamination, and the reactions are conducted under NAP conditions. The reaction cell is isolated from the UHV chamber with rubber face sealing, so that we can perform NAP experiments in the reaction cell and maintain an UHV environment for the chamber, and the rubber face sealing can maintain about eight orders pressure difference. Besides, a mass
spectrometer is also connected to the reaction cell, so we can monitor reactions with IR and mass spectroscopies simultaneously. We conducted testing related to the measurements of mass and IR spectroscopy with the NAP reaction cell. For mass spectroscopy, the signals of gaseous nitrogen and methanol can be measured with increased pressure inside the reaction cell and finally saturated
at about 1 mbar. For IR spectra testing, however, we found the absorption intensity is not enough to be measured with the reaction cell. Therefore, we introduced methanol to the entire chamber and monitored the IR absorption feature. The absorption feature of gaseous methanol could be observed at pressure above 1 mabr and became obvious as pressure up to 3 mabr. After evacuated methanol from the chamber, the gaseous methanol absorption feature then vanished.
In addition, we studied the reactivity of layered VSe2 toward methanol decomposition. The surface structures were characterized using reflective high energy electron diffraction (RHEED) and photoelectron spectroscopy (PES) while the reactions, intermediates, and gaseous products
were monitored by PES, near-ambient-pressure photoelectron spectroscopy (NAP-PES), and nearambient-pressure mass spectroscopy (NAP-MS). We generated the surface defects through Ar+ bombardment and controlled the defect concentration by tuning the Ar+ dosage. With PES spectra,
we observed that on VSe2 surface under UHV environment, the methanol decomposed and produced CHxO and CHx, and the production of these two intermediates altered with the surface defect concentration, where the better reactivity was presented at less defect concentration. Therefore, the surface reactivity of VSe2 can be manipulated via controlling the surface defect concentration through Ar+
bombardment. With NAP-PES spectra, the relative ratio of two
produced intermediates from methanol decomposition is opposite to the UHV case, implying some gaseous products were generated during the reaction and desorbed from the surface, and altered the relative ratio of intermediates remaining on surface. Moreover, based on measurements of
NAP-MS, the surface defects generated from Ar+ bombardment promoted the reactivity of VSe2 surface toward methanol decomposition under near ambient pressure conditions with several ultimately produced gaseous products, including D2(g), D2O(g)/CD4(g), CO(g), CD2O(g). | en_US |