Abstract:Heterogeneous solid base catalysts are highly expected
due to their
high activity and environmentally friendly nature in a variety of
reactions. However, the catalytic activity of traditional solid base
catalysts is controlled by external factors (such as temperature and
pressure), and regulation of the activity by in situ changing their
own properties has never been reported. Herein, we report a smart
solid base catalyst by chemically anchoring the photoresponsive azobenzene
derivative p-phenylazobenzoyl chlo… Show more
“…Thus far, azobenzenes have only been combined with UiO frameworks utilizing the photoswitch as linker backbone [47,48] or as pendant group. [49][50][51][52][53][54]…”
Understanding the interactions between hosts and guests in two‐component systems remains a formidable challenge due to the diverse array of adjusting factors at play. Particularly intriguing within the realm of two‐component systems are those incorporating a photoswitchable molecule within a porous metal‐organic framework (MOF) host. In such configurations, the non‐covalently attached guest molecule undergoes distinct physicochemical changes influenced by factors like guest structure, guest density, and the shape of the MOF pores. In this study, fluorinated azobenzenes (Fx‐AZB) were introduced into the rigid UiO‐66 host, and the resulting optical properties were examined with a focus on the degree of fluorination. The photoisomers of all examined compounds exhibited remarkable stability under repetitive light exposure, showing no signs of fatigue. Moreover, both photoisomers remained stable at room temperature, defying the typical T‐type photochromism associated with azobenzenes. Most notably, all fluorinated azobenzene derivatives displayed nearly complete photoswitching upon exposure to visible light within the UiO‐66 MOF host. This positions these composite materials as leaders in the realm of azobenzene‐based switch@MOF systems.
“…Thus far, azobenzenes have only been combined with UiO frameworks utilizing the photoswitch as linker backbone [47,48] or as pendant group. [49][50][51][52][53][54]…”
Understanding the interactions between hosts and guests in two‐component systems remains a formidable challenge due to the diverse array of adjusting factors at play. Particularly intriguing within the realm of two‐component systems are those incorporating a photoswitchable molecule within a porous metal‐organic framework (MOF) host. In such configurations, the non‐covalently attached guest molecule undergoes distinct physicochemical changes influenced by factors like guest structure, guest density, and the shape of the MOF pores. In this study, fluorinated azobenzenes (Fx‐AZB) were introduced into the rigid UiO‐66 host, and the resulting optical properties were examined with a focus on the degree of fluorination. The photoisomers of all examined compounds exhibited remarkable stability under repetitive light exposure, showing no signs of fatigue. Moreover, both photoisomers remained stable at room temperature, defying the typical T‐type photochromism associated with azobenzenes. Most notably, all fluorinated azobenzene derivatives displayed nearly complete photoswitching upon exposure to visible light within the UiO‐66 MOF host. This positions these composite materials as leaders in the realm of azobenzene‐based switch@MOF systems.
Solid strong base catalysts have attracted much attention for their excellent catalytic performance and environmental friendliness due to heterogeneous properties. However, this kind of catalyst usually needs a higher temperature to be activated. Therefore, it is still a challenge to obtain high-activity catalysts at lower fabrication temperatures. In this paper, a reductive catalyst support containing low-valence metal centers (Cr3+) was prepared. Through the redox reaction between the Cr3+ and KNO3, the basic sites can be produced at lower temperatures on the reductive support (Cr-MeIM). Thermogravimetry-mass (TG-MS) spectrometer results showed that the base precursor began to be transformed into basic sites at about a low temperature of 180°C. The solid base catalyst was applied into transesterification between ethylene carbonate (EC) and methanol. By using 0.05 g of catalyst for 3 h at 70°C, we obtained a dimethyl carbonate (DMC) yield of up to 60.9%, which means that the catalyst has high activity.
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