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Controlling the mode of reaction of a reactive intermediate such as an imine or iminium ion should enable the on‐demand selection of the final products from the same starting materials. The successful execution of such a strategy will reduce the time required to prepare diverse scaffolds. The imines derived from 4‐(allylamino)pyrimidine‐5‐carbaldehydes and anilines undergo Diels–Alder reactions to give pyrimido[4,5‐h][1,6]naphthyridines in high yields. A complete switch from the intramolecular aza‐Diels–Alder (IADA) path to an ene‐type cyclization reaction was achieved by simply adjusting the reaction conditions (amount of acid catalyst, solvent, and temperature). This newly introduced ene‐type cyclization reaction was used to prepare a series of epiminopyrimido[4,5‐b]azepines. To gain insight into the mechanism of the two reaction pathways, a DFT study was carried out. Theoretical calculations showed that under acidic conditions an iminium intermediate favors the low‐energy IADA pathway, which proceeds in a [4+ + 2] fashion. When acid is absent, the neutral imine intermediate favors the thermal ene‐type cyclization reaction, which takes place by transfer of an allylic proton from the allylic amine to imine, followed by a barrierless nucleophilic addition process between the in‐situ‐generated anionic allylic amine and iminium ion. Amine addition to the alkene finally gives the epiminopyrimido[4,5‐b]azepines.

TiO 2 has been widely used in ultraviolet (UV) photodetectors, but due to the large number of structural defects and strong band-to-band recombination of the exciton in TiO 2 , the devices usually have large dark current (I d ) and low light current (I l ), which seriously reduces the sensitivity and responsivity (R) of the TiO 2 based devices. In this work, carbon (C) quantum dots (QDs) are introduced into TiO 2 film to ameliorate these issues. Due to the difference of work function between TiO 2 nanoparticles and C QDs, the built-in electric field (E bi ) can be formed, which effectively facilitates the photogenerated exciton dissociation in the TiO 2 film under UV illumination. Meanwhile, the constructed depletion region in dark reduces the majority carrier density, thus decreasing the I d of the photodetector. Moreover, the E bi and depletion region will also contribute to the faster charge collection under UV illumination and recombination of the electron in dark, which is beneficial for the improved response/recovery speed of the device.

Hydrogenation of γ-valerolactone (GVL) to form 1,4-pentanediol (1,4-PDO) was performed over Co/ZrO2 catalysts with a Co metal loading of 15 wt. %. The calcination of Co/ZrO2 at high temperatures significantly promoted the catalytic activity irrespective of the decrease in the specific surface area. The 750 °C-calcined Co/ZrO2 with Co2+ species exhibited a high catalytic performance: a GVL conversion of 86.1% with a 1,4-PDO selectivity of 97.2% was achieved at 165 °C under 5 MPa H2 pressure.

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Depressurization combined with thermal stimulation is a promising method for gas hydrate production. Owing to its advantages of rapid uniform heating, microwave radiation is an efficient source of heat. However, the mechanisms of hydrate decomposition under depressurization combined microwave stimulation are currently unclear. In this study, methane hydrate was synthesized under 6 MPa and 2 °C, with hydrate saturation of approximately 42% in natural quartz sand. We then compared hydrate decomposition via rapid depressurization and piecewise depressurization, with or without microwave stimulation at 2.45 GHz and 400 W. When using the depressurization method alone, the hydrate decomposition rate increased with the depressurization amplitude. However, in the last stage of hydrate decomposition, the external flow of gas was hindered by the Jamin effect, especially under larger depressurization amplitudes; therefore, extremely low production pressure is not justified. When combined with microwave stimulation, both depressurization methods resulted in increased reservoir temperature within a few seconds, and microwave heating provided an extra driving force for hydrate decomposition. Furthermore, microwave heating was more effective when larger amounts of undecomposed hydrate remained after depressurization. When depressurization was combined with microwave stimulation, the average gas production rate at 100% gas production was 0.269−0.601 L/min, which was significantly higher than that for depressurization alone. However, the energy efficiency ratio was approximately 1, which has no practical value. Conversely, the average gas production rate at 90% gas production was 0.452−2.945 L/min and the energy efficiency ratio was 2.9−17.6. Under the combined method, gas hydrate decomposition at a production pressure of 1.9 MPa achieved the subtle balance between the average gas generation rate and energy efficiency. Thus, optimizing the gas production pressure and microwave stimulation time can improve the average gas production rate and energy efficiency ratio according to the reservoir hydrate conditions.