To probe the phase structure–reactivity relationship of A2B2O7 catalysts for the oxidative coupling of methane (OCM), three model La2B2O7 compounds with Ti4+, Zr4+, or Ce4+ at the B-site have been purposely designed. By decreasing the r A/r B ratios in the order of La2Ti2O7 > La2Zr2O7 > La2Ce2O7, typical monoclinic layered perovskite, cubic ordered pyrochlore, and disordered defective cubic fluorite phase are formed, respectively. The reaction performance of the catalysts based on CH4 conversion and C2 product yield follow the order of La2Ce2O7 > La2Zr2O7 > La2Ti2O7. It has been discovered that superoxide O2 – is the active oxygen species detected on all the catalysts and is responsible for the OCM reaction, whose amount follows also the sequence of La2Ce2O7 > La2Zr2O7 > La2Ti2O7. Moreover, the surface alkalinity related to the superoxide anions observes the same order. This testifies that the amount of surface superoxide O2 – determines the OCM reaction performance over the La2B2O7 compounds. On the basis of the characterization results, the formation of active O2 – species could follow two pathways. For La2Zr2O7 and La2Ce2O7 possessing intrinsic 8a oxygen vacancies, O2 – anions are formed by activating the oxygen species entering into the vacancies in the bulk and then migrating to the catalyst surface. For La2Ti2O7 possessing no oxygen vacancies, they are formed directly by transforming the O2 molecules adsorbed on its surface. Usually, the former pathway generates more abundant O2 – species than the latter one. La2Ce2O7 displays not only promising reaction performance in the low-temperature region, but also potent sulfur and lead poisoning resistance, thus having the potential for application after further optimization.

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The electrophilic halogenation of arenes is perhaps the simplest method to prepare aryl halides, which are important structural motifs in agrochemicals, materials, and pharmaceuticals. However, the nucleophilicity of arenes is weakened by the electron-withdrawing substituents, whose electrophilic halogenation reactions usually require harsh conditions and lead to limited substrate scopes and applications. Therefore, the halogenation of arenes containing electron-withdrawing groups (EWGs) and complex bioactive compounds under mild conditions has been a long-standing challenge. Herein, we describe Brønsted acid-catalyzed halogenation of arenes with electron-withdrawing substituents under mild conditions, providing an efficient protocol for aryl halides. The hydrogen bonding of Brønsted acid with the protic solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) enables this transformation and thus solves this long-standing problem.

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Ulva is the dominant genus in the green tide events and is considered to have efficient CO2 concentrating mechanisms (CCMs). However, little is understood regarding the impacts of ocean acidification on the CCMs of Ulva and the consequences of thalli’s acclimation to ocean acidification in terms of responding to environmental factors. Here, we grew a cosmopolitan green alga, Ulva linza at ambient (LC) and elevated (HC) CO2 levels and investigated the alteration of CCMs in U. linza grown at HC and its responses to the changed seawater carbon chemistry and light intensity. The inhibitors experiment for photosynthetic inorganic carbon utilization demonstrated that acidic compartments, extracellular carbonic anhydrase (CA) and intracellular CA worked together in the thalli grown at LC and the acquisition of exogenous carbon source in the thalli could be attributed to the collaboration of acidic compartments and extracellular CA. Contrastingly, when U. linza was grown at HC, extracellular CA was completely inhibited, acidic compartments and intracellular CA were also down-regulated to different extents and thus the acquisition of exogenous carbon source solely relied on acidic compartments. The down-regulated CCMs in U. linza did not affect its responses to changes of seawater carbon chemistry but led to a decrease of net photosynthetic rate when thalli were exposed to increased light intensity. This decrease could be attributed to photodamage caused by the combination of the saved energy due to the down-regulated CCMs and high light intensity. Our findings suggest future ocean acidification might impose depressing effects on green tide events when combined with increased light exposure.