An efficient catalyst for the direct hydroxylation of benzene to phenol with oxygen as the oxidant was developed by immobilizing the homogeneous vanadyl(IV) acetylacetonate (VO(acac)2) on SBA-15 in which the support surface was functionalized by (3-aminopropyl)triethoxysilane. The as-prepared catalyst was characterized by various techniques including field-emission scanning electron microscopy, X-ray diffraction, nitrogen adsorption and desorption, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results show that the homogeneous vanadium species can be successfully immobilized on the amine functionalized SBA-15 and exhibits better catalytic performance in the hydroxylation of benzene with oxygen compared to other catalysts reported in the literature. The phenol yield significantly depends on the reaction conditions. Under the optimized reaction conditions, the phenol yield can reach 13.3 %, and the as-fabricated V/NH2-SBA-15 shows better stability against leaching owning to strong interaction between vanadium atoms and amine group as compared to the V/SBA-15 sample.

In this work, porous ZnO photocatalysts were attempted to be prepared by a facile method, i.e. the thermal treatment of zeolitic imidazolate framework-8, and then characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy and nitrogen adsorption–desorption. It was found that the calcination temperature and time significantly influenced the morphology, composition and pore structure of ZnO. The photocatalytic activities of as-prepared ZnO powders were evaluated in the degradation of methylene blue (MB) under UV light in comparison with commercial anatase TiO2 and Degussa P25 TiO2. The surface area and crystallinity of porous ZnO obviously affected the photocatalytic activity of ZnO. The ZnO prepared at 500 °C for 5 h (ZnO-500-5) showed the highest photocatalytic activity, which was higher than that of the commercial anatase TiO2 and lower than that of Degussa P25 TiO2.Highlights► Porous ZnO powders can be obtained by thermal decomposition of ZIF-8. ► The morphology, structure and performance of porous ZnO can be controlled. ► ZnO-500-5 exhibits efficient photocatalytic activity for the degradation of MB.

A side-stream ceramic membrane reactor system was developed that can facilitate the in situ separation of ultrafine catalysts from the reaction mixture and make the production process continuous. Continuous hydroxylation of phenol to dihydroxybenzene over ultrafine titanium silicalites-1 (TS-1) was taken as a model reaction to evaluate the feasibility and performance of the membrane reactor system. The effects of membrane pore size and operation conditions (residence time, temperature, catalyst concentration, phenol/H2O2 molar ratio) on the performance of the reactor system were examined via single factor experiments. We demonstrated that the membrane pore size and operation conditions greatly affect the conversion, selectivity and filtration resistance. The phenol conversion and dihydroxybenzene selectivity remain stable at about 11% and 95% in a 20-h continuous run, respectively.

An integration process of ceramic membrane microfiltration (MF) with powdered activated carbon (PAC) was used to treat the oil-in-water emulsion in order to enhance the treatment efficiency. The role of PAC addition in flux enhancement mechanisms was investigated in detail. Results showed that the membrane flux for this system with particles was obviously higher than that of the oil-in-water emulsion alone. Combined with FESEM and EDS analyses, it was concluded that the gel layer formed on the membrane surface could be obviously reduced due to the mechanical scouring effect of particles according to the estimation of hydrodynamic forces, resulting in a higher membrane flux. The addition of PAC had no obvious effect on the removal efficiency of TOC and p-xylene, and they were removed about 96% in all cases. In short, the results of the present study demonstrated that the use of PAC as an additive in the integrated MF-PAC system was effective to mitigate membrane fouling and as a result increased the membrane flux because of scouring action.Graphical abstractResearch highlights▶ MF-PAC coupled system is used for advanced treatment of oil-in-water emulsion. ▶ Adding PAC reduces fouling and improves membrane flux because of scouring effect. ▶ Adding PAC has no obvious effect on the removal efficiency of TOC and p-xylene.

A new route towards phenol production by one-step selective hydroxylation of benzene with hydrogen peroxide over ultrafine titanium silicalites-1 (TS-1) in a submerged ceramic membrane reactor was developed, which can maintain the in situ removal of ultrafine catalyst particles from the reaction slurry and keep the process continuous. The effects of key operating parameters on the benzene conversion and phenol selectivity, as well as the membrane filtration resistance were examined by single factor experiments. A continuous reaction process was carried out under the obtained optimum operation conditions. Results showed that the system can be continuously and stably operated over 20 h, and the benzene conversion and phenol selectivity kept at about 4% and 91%, respectively. The ceramic membrane exhibits excellent thermal and chemical stability in the continuous reaction process.A one-step continuous synthesis route of phenol by hydroxylation of benzene with hydrogen peroxide over ultrafine TS-1 in a submerged ceramic membrane reactor is developed. The operation conditions have important impacts on the benzene conversion, phenol selectivity and filtration resistance. The optimum operation conditions can be obtained by balancing their effects on the catalytic properties and separation efficiency. The benzene hydroxylation with hydrogen peroxide over TS-1 can be continuously run over 20 h in the submerged ceramic membrane reactor and the ceramic membrane exhibits excellent stability in the reaction system.Download full-size image

•The microstructure of Pd@ZIF-L strongly depends on the synthesis temperature.•High temperature favors the increase of Pd loading.•High temperature is not beneficial for the maintaining of ZIF-L framework.•The Pd loading and microstructure are responsible for the catalytic activity.The Pd@ZIF-L catalysts with uniform crosshair-star shape and a size of about 20 μm were synthesized by an assembly method, in which a two-dimensional layered zeolitic imidazolate framework-L (ZIF-L) was used as the support to immobilize Pd nanoparticles. Their catalytic activities were evaluated by the catalytic reduction of p-nitrophenol to p-aminophenol. The results highlight that the physical-chemical and catalytic properties of the Pd@ZIF-L catalysts are greatly affected by the synthesis temperature. The temperature variation can make the catalysts transform from two-dimensional flakes to zero-dimensional spheres. High temperature is beneficial for increasing Pd loading and encapsulating Pd nanoparticles within the ZIF-L matrix. However, under the temperature larger than 30 °C, the dense dia(Zn) structures are formed. Increasing Pd loading in the Pd@ZIF-L catalysts leads to a significantly higher p-nitrophenol conversion. The relative dense structure of the as-synthesized catalysts makes p-nitrophenol access the active centers difficultly and a lower catalytic activity is observed. These findings would aid the development of high-performance Pd@ZIF-L catalysts.The structure, morphology, size, Pd loading and catalytic activity of the Pd@ZIF-L catalysts can be controlled by adjusting the synthesis temperature during the assembly process.