HCHO has been confirmed as an active intermediate in the methanol‐to‐hydrocarbon (MTH) reaction, and is critical for interpreting the mechanisms of coke formation. Here, HCHO was detected and quantified during the MTH process over HSAPO‐34 and HZSM‐5 by in situ synchrotron radiation photoionization mass spectrometry. Compared with conventional methods, excellent time‐resolved profiles were obtained to study the formation and fate of HCHO, and other products during the induction, steady‐state reaction, and deactivation periods. Similar formation trends of HCHO and methane, and their close correlation in yields suggest that they are derived from disproportionation of methanol at acidic sites. In the presence of Y2O3, the amount of HCHO changes, affecting the hydrogen‐transfer processes of olefins into aromatics and aromatics into cokes. The yield of HCHO affects the aromatic‐based cycle and the formation of ethylene, indicating that ethylene is mainly formed from the aromatic‐based cycle.

Desorption electrospray ionization (DESI) mass spectrometry imaging (MSI) can simultaneously record the 2D distribution of polar biomolecules in tissue slices at ambient conditions. However, sensitivity of DESI-MSI for nonpolar compounds is restricted by low ionization efficiency and strong ion suppression. In this study, a compact postphotoionization assembly combined with DESI (DESI/ PI) was developed for imaging polar and nonpolar molecules in tissue sections by switching off/on a portable krypton lamp. Compared with DESI, higher signal intensities of nonpolar compounds could be detected with DESI/PI. To further increase the ionization efficiency and transport of charged ions of DESI/PI, the desorption solvent composition and gas flow in the ionization tube were optimized. In mouse brain tissue, more than 2 orders of magnitude higher signal intensities for certain neutral biomolecules like creatine, cholesterol, and GalCer lipids were obtained by DESI/PI in the positive ion mode, compared with that of DESI. In the negative ion mode, ion yields of DESI/PI for glutamine and some lipids (HexCer, PE, and PE-O) were also increased by several-fold. Moreover, nonpolar constituents in plant tissue, such as catechins in leaf shoots of tea, could also be visualized by DESI/PI. Our results indicate that DESI/PI can expand the application field of DESI to nonpolar molecules, which is important for comprehensive imaging of biomolecules in biological tissues with moderate spatial resolution at ambient conditions.

Methyl radicals (CH3 •) are the key intermediates in the heterogeneous–homogeneous reaction processes of catalytic oxidative coupling of methane (OCM). Here, by applying in situ synchrotron-based vacuum ultraviolet photoionization mass spectrometry, we quantitatively detected CH3 • being desorbed from various metal oxides and validated the CH3 •-generating capability as an effective descriptor for the catalytic performance of the metal oxides in OCM. It is found that the C2 yield is linearly correlated to the amount and the desorption temperature of CH3 •, with the better OCM catalyst showing stronger CH3 • intensity and lower CH3 • desorption temperature. Furthermore, experimental characterizations together with density functional theory calculations suggest that the intrinsic electronic properties of metals and the subsequent generated electrophilic oxygen species are the decisive factors for CH3 • generation. Then, the CH3 •-generating capability can bridge the gap between the OCM performance and the structure of the catalyst and help us better understand the intrinsic structure–performance relationship in OCM over metal oxide catalysts.