Atom dispersion in metal supported catalysts is vital as it structurally accounts for their catalytic performances. Since practical catalysts normally present structural diversity, such as the coexistence of single atoms, clusters, and particles, traditional spectroscopy methods including chemisorption, titration, and Xray absorption, however, provide only an averaged description about the atom dispersion but are not able to distinguish localized structural divergence. In this work, through developing a methodology of electron-microscopy-based atom recognition statistics (EMARS), catalyst dispersion has been redefined at atomic precision in real space via the statistically counting 18 000+ Pt atoms for a Pt/Al 2 O 3 industrial reforming catalyst. The EMARS results combined with in situ microscopy evidence disclose that the activity for aromatics production quantitatively correlates with the density of Pt single-atoms, while Pt clusters contribute no direct activity but could kinetically transform into single-atoms when being heated under an oxidative atmosphere. Compared to EMARS, the traditional hydrogen−oxygen titration method is found to induce serious bias in the Pt dispersion in reference to actual activity. This distinctive capability of EMARS for metal dispersion quantification offers a possibility of directly identifying the catalysis roles of different metal species in a practical catalyst via atomresolved statistics.
Herein,
a dual-modal fluorescent/colorimetric “Signal-On” nanoprobe
based on PCN-222 nanorods (NRs) toward phosphate was proposed for
the first time. Due to the high affinity of the zirconium node in
PCN-222 NRs for phosphate, the structure collapse of PCN-222 NRs was
triggered by phosphate, resulting in the release of the tetrakis(4-carboxyphenyl)porphyrin
(TCPP) ligand from PCN-222 NRs as well as the enhancement of fluorescence
and absorbance signals. The PCN-222 NR-based nanoprobe could be employed
for phosphate detection over a wide concentration range with a detection
limit down to 23 nM. The practical application of the PCN-222 NR-based
nanoprobe in real samples was evaluated. Moreover, benefitting from
the good biocompatibility and water dispersibility of PCN-222 NRs,
this nanoprobe was successfully employed in the intracellular imaging
of phosphate, revealing its promising application in the biological
science. The present work would greatly extend the potential of nanostructured
MOFs in the sensing and biological fields.
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