Crystalline covalent organic frameworks (COFs) materials have good performance in photocatalytic conversions due to their excellent photoelectric properties in recent years. here, two new conjugated pyrene-based covalent organic frameworks (COFs), namely PyDF-COF and PyBMT-COF, were prepared through condensation polymerization of 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraaniline and 2,5-difluoroterephthalaldehyde or 2,5-Bis(methylthio)terephthalaldehyde, respectively. Highly selective aerobic hydroxylation of arylboronic acids can occur smoothly with high yields and a wide range of substrate universality. Compared with PyDF-COF, PyBMT-COF demonstrates a more efficient ability for this aerobic hydroxylation, indicating electron-donating thiomethyl groups of PyBMT-COF are more favorable to enhance distribution of electron cloud than electron-withdrawing fluorine groups of PyDF-COF, which make the PyBMT-COF more easily afford holes and electrons (h+-e-) separation, more effectively absorb visible light, and own narrower bandgap energy, higher photocurrent response, longer fluorescent lifetime and lower electrochemical impedance.

Herein, the Co-MMT (Co3O4-montmorillonite) catalysts were prepared by coordination-deposition (Co(0.015)-MMT-2(CD)) and deposition-precipitation method (Co(0.015)-MMT-2 (DP)) for the N2O direct decomposition, respectively. The structure, texture, and surface properties of the catalysts are characterized by XRD, TEM, FT-IR, Raman, XPS, and so on. The results show that compared with Co(0.015)-MMT-2(DP), Co(0.015)-MMT-2(CD) achieves barrier dispersion of active phase (Co3O4) by using the layer structure of montmorillonite and has a smaller Co3O4 crystal size, richer oxygen vacancy and higher content of Co2+Oh. In addition, the results of DFT calculation and kinetic calculation indicate that Co2+Oh possesses higher reaction activity than Co2+Td and Co3+Oh, and the TOF value of Co(0.015)-MMT-2(CD) at 400 ℃ is 3 times higher than that of Co(0.015)-MMT-2(DP). Therefore, the Co(0.015)-MMT-2(CD) catalyst shows excellent catalytic activity and tolerance to impurity gases (H2O, NO, and O2), and it can maintain 100% conversion at least 50 h for the direct catalytic decomposition of N2O.

A family of heterojunction photocatalysts C60/TpPa have been constructed from fullerenes (C60) and TpPa-1 via in-situ solvothermal method firstly. The photocatalytic activity toward CO2 of C60/TpPa has been evaluated through the gas-solid reaction system under pure CO2 and low concentration CO2 (10 %) atmosphere, respectively. The results show that the maximum CO formation rates for C60/TpPa are as high as 48.16 μmol·g−1·h−1 and 90.25 μmol·g−1·h−1 under pure CO2 and 10 % CO2 environment, respectively. The attractive experimental phenomenon is assigned to the existence of CO groups in TpPa-1. Due to the presence of Z-scheme heterojunction, the separation of photoexcited electrons and holes is effectively enhanced, and the photocatalytic performances are significantly improved. This work suggests that the construction of COF-based photocatalysts with heterojunction for efficient photoreduction of CO2 is a promising strategy.

[Cu(acac)(phen)(H2O)](ClO4) and [Cu(acac)(bipy)(H2O)](ClO4) catalysts were prepared by the immobilization of mixed-ligand complexes on graphene oxide derivatized with monochloroacetic acid. These catalysts were characterized through an ensemble of techniques including XRD, FTIR, Raman, and XPS while the catalytic behavior has been investigated in the oxidation of cyclohexene, 1-octene and glycerol in the presence of molecular oxygen. Cyclohexanone was the dominant product in the oxidation of cyclohexene resulting in selectivities higher than 50% for a conversion of 14.5%. The turnover frequencies were pretty high, namely, 4.5 h−1 for [Cu(acac)(phen)(H2O)](ClO4) and 2.3 h−1 for Cu(acac)(bipy)(H2O)](ClO4). The oxidation of 1-octene also occurred with a pretty high selectivity in 2-octanol as the main product. The role of copper in the oxidative dehydrogenation of glyceric acid towards tartronic acid was as well confirmed. Noteworthy, these catalysts were stable and their recycling occurred with no change in the conversion or selectivity.

Supported Pd single-atom alloy (SAA) catalysts are selective in acetylene semi-hydrogenation. However, it is a challenge to prepare Pd SAA where Pd single atoms dispersed on the outmost surface of the catalysts because the Pd atoms on Pd SAA prepared by conventional impregnation distribute inside the alloyed particle or on the support surface after activation. In this work, we firstly synthesized Ni/SiO2 nanocatalysts by impregnation, followed by H2 reduction to generate metal Ni particles on SiO2. Subsequently, Pd single atoms are selectively deposited on the Ni particle surface by atomic layer deposition (ALD). The Pd species on the Pd1Ni/SiO2 prepared by ALD dispersed on the outmost surface of catalyst, presenting the improved catalytic performances in acetylene hydrogenation, as compared to a reference Pd1Ni/SiO2 catalyst prepared by impregnation. The Pd1Ni/SiO2 catalyst prepared by ALD with 5 cycles (0.04 wt. %Pd, 5c-Pd1Ni/SiO2) shows both superior hydrogenation activity (92 %) and selectivity (88 %) under mild temperature (80 °C) in the selective semi-hydrogenation of acetylene. Moreover, the specific activity of the 5c-Pd1Ni/SiO2 catalyst is the highest, as compared to the catalysts reported in literature. Therefore, we conclude that the metal single atoms on metal SAA catalyst prepared by ALD locate on the outmost surface of the catalyst, presenting the unusual catalytic performances in catalysis.

Rutile TiO2 was identified as a suitable support for nickel than the anatase form in the selective conversion of levulinic acid (LA) to γ-valerolactone (GVL) with a 20-fold rate enhancement. TEM-HAADF results revealed a high degree of Ni encapsulation by titania species on the anatase that resulted in lower LA conversion with a high selectivity of angelica lactones. While nickel plateaus with protruding particles partially covered by TiOx overlayers on a rutile surface was the reason for the higher rate of GVL. CO chemisorption results indicated a lower uptake on 10 wt%Ni/TiO2-anatase than on the 10 wt%Ni/TiO2-rutile catalyst and a high rate of hydrogen spillover was manifested by rutile TiO2 supported Ni catalyst than its counterpart anatase. Variations in the crystal phase of TiO2 and their interaction with nickel could substantially influence the GVL formation. High intrinsic activity of 10 wt%Ni/TiO2-800(R) was explained and discussed using surface and bulk characteristics of the catalysts.

The second C−H bond cleavage in methane to form methylene (CH2*) from methyl (CH3*) is the rate-limiting step for the direct non-oxidative methane coupling to ethylene over gallium-nitride catalysts. Herein, we use isotope labelled experiments, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 13C solid state-NMR, as well as kinetic modelling to elucidate the reaction mechanism. Our experiments showed that supported GaN/SBA-15 had more aliphatic surface intermediates (CH3* and CH2*) than unsupported GaN catalysts, which had higher amounts of aromatics intermediates and coke deposition. Isotope labelling experiments and the kinetic study confirmed that the most likely pathway is via the fast abstraction of the first H from CH4 to form methyl (CH3*) surface intermediates, followed by the slow second C−H bond cleavage to form methylene (CH2*) and subsequent coupling to ethylene. The intrinsic activation energy predicted by kinetic modelling was rather low at around 20 kJ mol−1.

Converting biomass derived levulinic acid (LA) to γ-valerolactone (GVL) through catalytic transfer hydrogenation, using Lewis acidic catalysts and alcohols as hydrogen donors, is an important route for biomass valorization. Zeolites containing Lewis acidic metal ions have been widely studied for catalytic transfer hydrogenation of LA. On the other hand, zeolites themselves have Al-Lewis acid sites, inherent to their aluminosilicate framework, and these sites can be generated and tuned through simple post-synthesis methods. The present study shows that properly tuned Al sites in Y zeolites can catalyze LA to GVL conversion, and the key requirement for this conversion is creating more penta-coordinated Al sites in the catalyst. In order to establish this, a series of thermally-treated (500–800 °C) and steam-treated (500 and 700 °C) Y zeolites were prepared, characterized by X-ray diffraction, N2 adsorption, temperature programmed desorption of NH3, 27Al MAS NMR spectroscopy and pyridine adsorption – FTIR spectroscopy and then tested for LA to GVL conversion. Thermal dealumination of NH4Y zeolite at 700 °C (TY700) gave the highest percentage (21%) of penta-coordinated Al and it was found to be more selective (∼94%) in forming GVL than other catalysts studied under the optimized conditions. The turnover frequency of formation GVL, (TOFGVL) from isopropyl levulinate (IPL) on TY700 was three times higher than that of TY500 (NH4Y thermally treated at 500 °C). During the reaction, acid sites of the zeolite catalyze esterification of LA with isopropyl alcohol and hence LA is readily converted to isopropyl levulinate and then Meerwein–Ponndorf–Verley (MPV) reduction of IPL leads to the formation of isopropyl 4-hydroxy pentanoate, which undergoes lactonization to form GVL. Based on the experimental results, a plausible reaction mechanism involving the penta-coordinated Al Lewis acid sites and -Al-OH group was proposed.

Nanometric Pt clusters show promising applications in alkane reforming. However, stabilizing the nanometric Pt clusters on the zeolite at high temperature is still challenging. Herein, we fabricate the zinc-assisted nanometric Pt cluster stabilized on the KL zeolite using atomic layer deposition technology. The deposition of Zn significantly enhances the stability of nanometric Pt cluster and, therefore, makes PtZn3/KL as a robust n-heptane dehydrocyclization catalyst. Systematic characterizations combined with DFT calculations disclose that the deposited Zn species donate electrons to Pt and thus promote the cleavage of C-H bond of n-heptane and facilitate the dehydrocyclization of alkene-like intermediates (σC7=) to aromatics. In addition, an easier desorption of toluene benefits the high reactivity of PtZn3/KL catalyst by preventing the dehydrogenation and cleavage of C-C bonds to form the by-products or coke deposition. This method for enhancing the stability of nanometric Pt clusters paves a way for designing high-efficient dehydrocyclization catalysts.

The morphology effect of TiO2 on the dispersion of molybdena species and the performance of the resulting MoOx/TiO2 catalysts in selective oxidation of isobutene to methacrolein were examined. Two-dimensional MoOx monolayers in Mo–O–Mo bonds were well dispersed on TiO2 nanosheets that were preferentially enclosed by the {001} facets. However, aggregated MoOx clusters enriched in terminal MoO bonds were formed over TiO2 nanospindles dominated by the {101} facets. The superior performance of the MoOx monolayers, regarding activity, selectivity and stability, was ascribed to the synergetic effect between MoOx monolayers and TiO2 (001) facets.

Titania-supported ruthenium (Ru/TiO2) is an established catalyst for the hydrogenation of carbon dioxide to methane (Sabatier reaction). Chlorine contamination, owed to the RuCl3 precursor, is demonstrated to have a detrimental impact on methanation activity. After calcination and reduction the catalyst contains residual chlorine, shown by XPS. An aqueous ammonia wash removes Cl without leaching Ru. The washed catalysts exhibit improvements in CH4 site-time yields. Low Ru loading catalysts encounter the greatest activity enhancements after washing (∼4.5–fold). DFT calculations indicate that chlorine and CO2 directly compete for adsorption on Ru step sites, with Cl impeding the adsorption of CO2 at under-coordinated sites and at higher Cl coverages. H2-chemisorption/TPR show that Cl removal lowers the onset of low temperature H2 dissociation on Ru. DRIFTS provide evidence that the removal of Cl facilitates low temperature dissociative binding of CO2, indicated by the formation of surface bound linear CO species.

Global industrial development and increased energy demand are key contributors to the rise in CO2 emissions and global climate change. It is therefore necessary to build a sustainable energy infrastructure that would be based on hydrogen from renewable energy sources. Herein, we first introduce the different methods for H2 generation, including photocatalysis with TiO2 as one of the most widely used photocatalysts. The various processes occurring on irradiated TiO2 and their contribution to photocatalytic H2 efficiency are discussed. The next part deals with the best techniques for material engineering, including self-doping, loading with co-catalysts, doping with metals and non-metals, and heterojunction structures. The last part displays the effects of external conditions that positively influence photocatalytic H2 production, especially thermo- and mechanically-assisted photocatalysis. As part of this special issue, this mini-review summarizes most of the investigations carried out in this field by the groups led by Prof. Bahnemann.

A photocatalytic paint for the air decontamination was tested under different operating conditions in a reaction chamber that simulates an indoor room. An experimental design was applied to cover a wide range of indoor air conditions (irradiation level, air flow rate, relative humidity and inlet pollutant concentration). It was proposed to develop a first principles model capable of predicting the outlet contaminant concentration from the continuous reaction chamber or the evolution of the reactant concentration operating the chamber in batch mode. The main inputs for the model were: i) optical properties of the paint, ii) characteristics and dimensions of the radiation source, iii) dimensions and operating conditions of the reaction chamber, and iv) intrinsic photocatalytic kinetics previously determined. The developed models showed a very good agreement with experimental measurements. The proposed methodology could be extended considering all indoor environmental conditions to simulate air decontamination in real applications of photocatalytic paints.

The behavior of palladium-phosphorus catalysts deposited on a Na-ZSM-5 zeolite support, in the direct synthesis of hydrogen peroxide under mild conditions has been studied. It was found that elemental phosphorus exerts a promoting effect on the activity and selectivity of Pd catalysts for synthesizing H2O2. A direct relationship between the P:Pd ratio (in the range P:Pd = 0: 1.0) and the activity of the catalysts is shown. The influence of phosphorus on the properties of palladium catalysts in side reactions: decomposition and hydrogenation of H2O2 is considered. The chemical and phase composition of Pd-P particles was studied by ICP, HRTEM, electron diffraction, and XRD methods. The modifying effect of phosphorus on the properties of Pd catalysts in the direct synthesis of H2O2 is associated with the formation of solid solutions between palladium and phosphorus, an increase in the dispersion, and the surface roughness of Pd-P particles.

Cationic manganese (MnP - [Mn(T4MPyP)]5+) and anionic iron (FeP - [Fe(TDFSPP)]3–) metalloporphyrins in conjunction with zinc oxide of different morphologies, were synthesized. After characterization by different instrumental techniques, the metalloporphyrins were immobilized on the obtained zinc oxide and the catalysts were evaluated regarding the oxidation of cyclohexane, using iodosylbenzene (PhIO) as model oxidant. In the absence of light, the activities of FeP/ZnO were higher than those obtained by neat ZnO and MnP/ZnO. Furthermore, under the reaction conditions of 1:100:1000 catalyst/oxidant/substrate, with acetonitrile as solvent, for 1 h at 25 °C without any radiation source, the reactions were selective for ketone. The same occurred for the neat FeP under homogeneous conditions. In contrast, when the reaction proportions were changed to 1:20:1000 catalyst/oxidant/substrate and when the catalyst amount was increased 10 times, the selectivity was for alcohol. Under irradiation with a dichroic halogen lamp (50 W), all the systems containing FeP showed higher selectivity for alcohol, while when MnP was used, increments like those with FeP were not observed, probably due to the structural differences between FeP and MnP. This FeP to MnP replacement led to spectral differences that might have been responsible for the inability of MnP to interact efficiently with the radiation emitted by the dichroic halogen lamp as well as promoting the higher amount of ketone produced in comparison with the FeP/ZnO system.

Heck reaction is one of the effective routes to form C-C bond, however the process still suffers problems from the separation and low-temperature activity of catalysts. Herein, Pd nanoparticles supported on SiC was prepared by a sample impregnation-reduction process. The Pd/SiC photocatalyst exhibited a high iodobenzene conversion of 99.6 % with 100 % selectivity to methyl cinnamate under visible light irradiation at 40 ℃. The excellent performance is due to the good light absorption ability of Pd/SiC and effective charge separation through Mott-Schottky junction between Pd and SiC. The electron-rich Pd nanoparticles are favorable to activate C-I bond of iodobenzene, thus enhancing the photocatalytic activity for Heck reaction of iodobenzene and methyl acrylate.

Dehydration of biomass-derived 1,4-butanediol (1,4-BDO) is an attractive approach to synthesizing 1,3-butadiene (BD), which is a useful monomer for various polymers and currently produced via naphtha cracking. Cerium oxide (CeO2) with weak acid-base bifunctionality promoted the dehydration of 1,4-BDO to BD in 66% yield with 80% selectivity under the optimized conditions. The selectivity given by the CeO2 catalyst was influenced by the calcination temperatures, since the acid-base bifunctionality and reducibility of CeO2, which were examined temperature-programmed analyses, were altered. In stark contrast, the catalysts with strong acid sites exemplified by SiO2-Al2O3 and H-type mordenite (H-MOR) were inappropriate for this reaction since they produced tetrahydrofuran as a major product. The control experiments using a set of substrates suggested that 3-butene-1-ol was the main intermediate in the 1,4-BDO-to-BD dehydration, and its isomer of 2-butene-1-ol was also involved in the reaction but rather triggered the undesired side reactions to form butyraldehyde and ketones.

The main problems of liquid-phase oxidation of methylarenes to benzaldehydes are that the catalytic reaction rate is slow, benzaldehydes are easily over-oxidized to form benzoic acids, and a large amount of solvent is required. These problems make it difficult to realize the liquid phase catalytic oxidation of methylarenes to benzaldehydes in industrial production. Here, we report the catalytic oxidation of toluene to form benzaldehyde, by using N-hydroxyphthalimide (NHPI) as the radical catalyst, sheet-like Co-Mn-Al oxides (CMA-n) as the redox catalyst, and 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as the solvent. CMA-n/NHPI was found to be highly active in catalyzing the oxidation of toluene to benzaldehyde. The use of HFIP as the solvent prevents the over-oxidation of benzaldehyde to benzoic acid. In addition, the reaction proceeded at a high concentration of toluene. The conversion rate of toluene reached 5826 μmol g−1 h−1, and the generation rate of benzaldehyde reached 4049 μmol g−1 h−1.

A string of niobium-iron composite oxides with varying Nb/Fe ratios and calcination temperatures were produced and utilized to remove mixed contaminants (500 ppmv chlorobenzene and 500 ppmv toluene in air), and the structure/texture of catalytic materials were systematically characterized. The findings of the structure-performance study revealed that the physicochemical qualities of Nb2O5-Fe2O3 were greatly enhanced than pure metal oxide. The presence of iron oxide hindered the crystallization of niobium oxide, which aided in the uniform dispersion of niobium-iron components into each other. Forming FeNbO4 at Nb/Fe molar ratio of 1/2 effectively improved the thermal stability of catalyst, withstood short-time thermal shock below 850 °C. The formation of niobium-iron composite oxides improved the specific surface area, optimized the pore size distribution, increased surface acid centers, enhanced reduction/oxidation cycle, and promoted metal-metal interaction for the Nb-Fe-O catalysts. At 320 °C, the catalytic degradation efficiency of 1Nb2Fe-500 could approach 90% for chlorobenzene and 85% for toluene, and it could sustain this efficiency for at least 80 h without evident deactivation, with a high CO2 selectivity of 86%. Furthermore, the Nb-Fe-O catalysts met the environmentally benign and low-cost requirements for environmental catalysis.

This study investigated the effect of Ag-Bi co-modified nanostructured TiO2 on photodegradation of gaseous formaldehyde (HCHO). The Ag/Bi-TiO2 materials were synthesized using the hydrothermal method with various concentrations of Ag (0–2 %). The synthesized materials were characterized using XRD, SEM, TEM, EDS, PL, UV-Vis, XPS, and ESR. Their performance under visible-light irradiation was found to be significantly influenced by the amount of Ag doping, the calcination temperature and the air contact area. The results demonstrated higher Ag doping greatly enhanced the degradation of HCHO. The photocatalytic degradation efficiency of HCHO over 2%Ag/Bi-TiO2 reached 87.5 %, which was significantly higher compared to Bi-TiO2 (74.0 %) and TiO2 (65.6 %), and the concentration of HCHO decreased from 1.069 to 0.134 mg/m3 within 48 h. The heterostructure of Ag2O/Ag and Bi-TiO2 facilitated effective electron transfer and suppressed the recombination of electron-hole pairs. The enhanced adsorption of visible-light and the improved photocatalytic performance were attributed to the synergistic effect of surface hydroxyl and adsorbed oxygen.