The photoreduction of carbon dioxide (CO₂) into renewable synthetic fuels is an attractive approach for generating alternative energy feedstocks that may compete with and eventually displace fossil fuels. However, it is challenging to accurately trace the products of CO₂ photoreduction on account of the poor conversion efficiency of these reactions and the imperceptible introduced carbon contamination. Isotope-tracing experiments have been used to solve this problem, but they frequently yield false-positive results because of improper experimental execution and, in some cases, insufficient rigor. Thus, it is imperative that accurate and effective strategies for evaluating various potential products of CO₂ photoreduction are developed for the field. Herein, we experimentally demonstrate that the contemporary approach toward isotope-tracing experiments in CO₂ photoreduction is not necessarily rigorous. Several examples of where pitfalls and misunderstandings arise, consequently making isotope product traceability difficult, are demonstrated. Further, we develop and describe standard guidelines for isotope-tracing experiments in CO₂ photoreduction reactions and then verify the procedure using some reported photoreduction systems.

Conversion of polyethylene (PE) into ethylene and propylene will enable closed-loop recycling of plastics. Conventional catalytic cracking of PE is restricted by kinetic entanglement between the formation of main products and by-products, limiting ethylene and propylene yields to less than 25%. Here we address this challenge with a kinetic decoupling–recoupling (KDRC) strategy, achieving yields of ethylene and propylene up to 79% from PE conversion using a tandem reactor with dual zeolite catalysts. Reaction kinetics analysis, synchrotron-based vacuum ultraviolet photoionization mass spectrometry and in situ neutron powder diffraction reveal that KDRC decouples kinetics of PE cracking to intermediates (butenes and pentenes) in the first stage and synchronizes this process with dimerization–β-scission reactions in the second stage. This synchronization minimizes by-products and enhances ethylene and propylene production substantially. Combined with high catalytic stability, this KDRC strategy represents a robust pathway to combating plastic pollution via a circular economy.

Ambient mass spectrometry imaging (AMSI) has attracted much attention in recent years. As a kind of unlabeled molecular imaging technique, AMSI can enable in situ visualization of a large number of compounds in biological tissue sections in ambient conditions. In this review, the developments of various AMSI techniques are discussed according to one-step and two-step ionization strategies. In addition, recent applications of AMSI for lipid and metabolite analysis (from 2016 to 2021) in disease diagnosis, animal model research, plant science, drug metabolism and toxicology research, etc., are summarized. Finally, further perspectives of AMSI in spatial resolution, sensitivity, quantitative ability, convenience and software development are proposed.

Understanding the dynamic evolution of heterogeneous catalysts is crucial yet challenging for elucidating the structure-performance relationships and enabling rational catalyst design. Herein, we reveal that PtIn alloy clusters gradually evolve into Pt₃In intermetallic in response to propylene, the product of propane dehydrogenation (PDH) reaction. Specifically, a PtIn_1.0/SiO₂ catalyst has been fabricated, comprising sub-nanometric PtIn alloy clusters covered by an In⁰ overlayer, with In³⁺ species locating at the metal-support interface. During the PDH reaction propylene induces the evaporation of the In⁰ overlayer, thereby exposing Pt sites. After an induction period, the evolved Pt₃In intermetallic (average size ~1.3 nm) exhibits a C₃H₆ productivity of 145 mol g_Pt⁻¹ h⁻¹. The alloyed In⁰ species effectively dilute Pt-Pt ensembles, enhancing propylene selectivity, while the interfacial In³⁺ species inhibit aggregation of Pt₃In intermetallic, ensuring excellent catalytic stability. These findings underscore the critical role of product molecules in shaping active site evolution at the atomic scale.

Gallium-modified HZSM-5 zeolites are known to increase aromatic selectivity in methanol conversion. However, there are still disputes about the exact active sites and the aromatic formation mechanisms over Ga-modified zeolites. In this work, in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) experiments were carried out to study the behaviors of intermediates and products during methanol conversion over Ga-modified HZSM-5. The increased formaldehyde (HCHO) yield over Ga-modified HZSM-5 was found to play a key role in the increase in aromatic yields. More HCHO was deemed to be generated from the direct dehydrogenation of methanol, and Ga₂O₃ in Ga-modified HZSM-5 was found to be the active phase. The larger increase in aromatic production over Ga-modified HZSM-5 after reduction‒oxidation treatment was found to be the result of redispersed Ga₂O₃ with smaller size generating a larger amount of HCHO. This study provides some new insights into the internal driving force for promoting the production of aromatics over Ga-modified HZSM-5.