3,4-Dihydroisoquinolines are high-value chemicals, both as medicinally relevant compounds and as intermediates for the synthesis of 1,2,3,4-tetrahydroisoquinoline derivatives, which are widely regarded as privileged scaffolds in drug discovery. Though envisaged as a direct route, the partial oxidation of 1,2,3,4-tetrahydroisoquinolines to 3,4-dihydroisoquinolines is, however, very challenging due to the inherent tendency of these substrates toward over-oxidation to the aromatic isoquinolines. Herein, we have used 1,2,3,4-tetrahydroisoquinoline (THIQ) as a model substrate for its selective oxidative dehydrogenation to 3,4-dihydroisoquinoline (DHIQ) under heterogeneous photochemical conditions with titania-based photocatalysts. Among the materials tested, TiO2-P25 and CuNPs/TiO2-P25 have been found to be the best photocatalysts in terms of conversion and selectivity upon irradiation (369 nm) in acetonitrile, with oxygen as a terminal oxidant. Notably, high conversion and selectivity were also attained with TiO2-P25 in the presence of Cs2CO3 under air. Although pristine TiO2-P25 represents the simplest and most readily available photocatalyst, CuNPs/TiO2-P25 is clearly superior from a reusability standpoint, maintaining high conversions (97-96%) and excellent selectivities (97:3-96:4) over the first four cycles, and consistently outperforming TiO2-P25 in the oxidation of other amines. A detailed characterisation of this catalyst, combined with comprehensive mechanistic studies, supports a strong substrate-surface interaction that facilitates single-electron transfer oxidation of the former; accordingly, a consistent reaction mechanism has been proposed. A meticulous green chemistry assessment shows that, while TiO2-P25 displays the most favourable risk-factor score, CuNPs/TiO2-P25 provides the most balanced overall sustainability profile when risk factors, waste generation and recyclability are considered, and benchmarks favourably against previously reported photocatalytic methodologies. Overall, this study introduces an efficient and sustainable photocatalytic method that not only overcomes key limitations of previous systems, but also underscores the effectiveness and practicality of heterogeneous photochemical approaches under mild aerobic conditions.

The efforts to increase the active surface area of catalysts led to reduction of metal particle size, down to single metal atoms. This results in increasing importance of support-metal interactions. We demonstrate the mechanisms through which the support influences catalytic activity of nanoclusters: the support electronics, described by the O 2p energy level, and the support surface chemistry, determined by the density of Lewis base sites. Using Ru nanoclusters, our study shows that these parameters can be effectively captured within a single catalyst support descriptor (CSD). The apparent activation energy and turnover frequency (TOF) for the ammonia synthesis correlates strongly with CSD measured for the series Ru/MgO, Ru/Sc2O3, Ru/CeO2, Ru/La2O3, and Ru/Y2O3. Furthermore, the study demonstrates that CSD correlates linearly with the binding strength of N-Ru in nanocluster, thereby providing a direct link between the catalyst's surface chemistry and the nature of the support. The catalyst support descriptor developed in this study serves as a simple yet powerful tool for selecting the optimal support material to maximise the activity of metal nanoclusters without altering the metal itself.

Developing sustainable, efficient catalysts for the electrocatalytic reduction of CO2 to valuable products remains a crucial challenge. Our research demonstrates that combining tin with nanostructured carbon support leads to a dynamic interface promoting the transformation of microparticles to nanoparticles directly during the reaction, significantly increasing the formate production up to 5.0 mol h-1 g-1, while maintaining nearly 100% selectivity. Correlative electrochemistry-electron microscopy analysis revealed that the catalyst undergoes an in situ self-optimization during CO2 electroreduction. It has been found that changes in the catalyst are caused by the breakdown of Sn particles driven by electrochemical reactions. The process of pulverization typically results in a decrease in the catalytic activity. However, when Sn particles are pulverized and reach approximately 3 nm in size on the surface of the nanotextured carbon support, the efficiency of the catalyst is maximized. This enhancement occurs because the in situ-formed Sn nanoparticles exhibit better compatibility with the nanotextured support. As a result, the number of electrocatalytically active sites significantly increases, leading to a reduction in charge transfer resistance by more than 2-fold and an improvement in reaction kinetics, which is evidenced by changes in the rate-determining step. Collectively, these factors contribute to a 3.6-fold increase in the catalyst's activity while maintaining its selectivity for formate production.

Synergistic magic: copper single atom and nanocrystalline carbon nitride for selective CO 2 to methanol conversion.

The reaction of calcium carbide with water has been widely used as a source of acetylene for the synthesis of organic molecules. In contrast with this traditional approach, we use the CaC2 reaction under water-starved conditions and show reactions that involve a calcium acetylide intermediate, reminiscent of Grignard reaction intermediates, which are stabilized by the solvent. Using this reaction pathway may allow for new chemistry, finer reaction control, and safety by limiting the formation of acetylene gas during the reaction. For example, reaction with bromoarenes, readily yields the corresponding diaryl acetylene. Ruins of the building in Gatineau Park, Quebec, Canada where Thomas "Carbide" Willson used to manufacture calcium carbide, with some CaC2 rocks as an inset on the top left, and in white, the mechanism proposed. image

CO2 adsorption and its subsequent utilization represent a promising avenue for mitigating climate change. The conver-sion of CO2 into valuable and useful products like carbon monoxide, methane, and methanol offers significant economic benefits. However, due to the low reactivity of CO2, the incorporation of CO2 adsorbents alongside catalytic materials has been pivotal in increasing the concentration of CO2 molecules around the catalytic sites. This strategy frequently relies on the precise deposition of the catalyst onto the adsorbent material. In this work, we explore NU-1000, a zirconium-based metal-organic framework originally designed as a CO2 adsorbent, to act as a selective photocatalyst for gas-phase CO2 reduction to CH4. NU-1000 contains UVA light-absorbing chromophore linkers, endowing it with the dual functionality of CO2 adsorbent and photocatalyst, which is crucial for efficient CO2 reutilization. Our research showcases an easily reproducible, and greener synthesis method for NU-1000 using micro-waves. We study the activity of NU-1000, including a functionalised variant, in the gas-phase photoreduction of CO2 to CH4 at room temperature and atmospheric pressure with electrons and protons derived from water. Remarkably, both the native and functionalised MOFs exhibit a rate of 170 and 800 μmol∙g-1∙h-1, respectively, alongside an exceptional selectivity of over 99%. These findings represent some of the highest reported values for gas phase CO2 photoreduction under atmospheric conditions. Our results provide a foundation for exploring materials that can serve as both catalysts and sorbents in the photocatalytic transformation of CO2 to value-added products.

Perylene diimides (PDI) have an extraordinary ability to activate both energy and electron transfer process upon light excitation, however, their extremely low solubility has hindered their wide use as photocatalysts. Here, we show a series of supports developed to anchor PDI and to enable its use as a heterogeneous photocatalyst in diverse reactor set-ups. Inert, easy-to-handle, glass microspheres of various morphological and chemical properties were chemically functionalised with PDI to form an inorganic-organic hybrid material. Using the photo-oxidation of n-butyl sulfide as a benchmark reaction for the synthesis of sulfoxides, we show that immobilised PDI are highly active, outperforming reported homogeneous photosensitisers, and capable of reuse in both batch and flow reactors. Transferring the process from batch to flow resulted in a 10-fold reduction in irradiation time and an increase in the space-time-yield by a factor of 10 (0.04 vs 0.38 mmol-1 h-1 mL-1 batch vs flow). This work combines the remarkable photocatalytic properties of PDI with inert, easy to handle glass beads, producing hybrid materials that are reusable and can be adapted for performing heterogeneous photocatalysis in a range of scalable photochemical reactors.

Here, we discovered that Pd decorated TiO 2 (Pd@TiO 2 ) enables consecutive photocatalytic Sonogashira C−C coupling and hydrogenation steps by simply adjusting the excitation conditions of the reaction. We demonstrated that by‐products containing iodine species generated in the first reaction step can inhibit subsequent photocatalytic processes, but they can be easily removed from solution to enable a compatible synthetic sequence for new C−C bond formation under mild reaction conditions. This work incorporates heterogeneous photocatalysts into consecutive transformations, promoting elegant reactions while meeting the demands of green chemistry.

Water decontamination remains a challenge in severaldevelopedand developing countries. Affordable and efficient approaches areneeded urgently. In this scenario, heterogeneous photocatalysts appearas one of the most promising alternatives. This justifies the extensiveattention that semiconductors, such as TiO2, have gainedover the last decades. Several studies have evaluated their efficiencyfor environmental applications; however, most of these tests relyon the use of powder materials that have minimal to no applicabilityfor large-scale applications. In this work, we investigated threefibrous TiO2 photocatalysts, TiO2 nanofibers(TNF), TiO2 on glass wool (TGW), and TiO2 inglass fiber filters (TGF). All materials have macroscopic structuresthat can be easily separated from solutions or that can work as fixedbeds under flow conditions. We evaluated and compared their abilityto bleach a surrogate dye molecule, crocin, under batch and flow conditions.Using black light (UVA/visible), our catalysts were able to bleacha minimum of 80% of the dye in batch experiments. Under continuousflow experiments, all catalysts could decrease dye absorption undershorter irradiation times: TGF, TNF, and TGW could, respectively,bleach 15, 18, and 43% of the dye with irradiation times as shortas 35 s. Catalyst comparison was based on the selection of physicaland chemical criteria relevant for application on water remediation.Their relative performance was ranked and applied in a radar plot.The features evaluated here had two distinct groups, chemical performance,which related to the dye degradation, and mechanical properties, whichdescribed their applicability in different systems. This comparativeanalysis gives insights into the selection of the right flow-compatiblephotocatalyst for water remediation.

Selective semi-oxidation of tetrahydroisoquinoline (THIQ) leads to a valuable dihydroisoquinoline (DHIQ) derivative via singlet oxygen photooxidation process. Typical photosensitisers (i.e., Ru complexes) can activate the reaction even under heterogeneous conditions that facilitate catalyst separation and reusability. In contrast to DHIQ, THIQ acts as an efficient singlet oxygen quencher driving the reaction selectivity. The reaction can also be facilitated by semiconductor catalysts such as MoCo@GW, a glass wool-based catalyst that is easy to separate and reuse and compatible with flow photochemistry. Its role is to mediate the formation of isoquinoline (IQ) and thus an in situ-generated singlet oxygen catalyst. Laser flash photolysis with NIR detection provides proof of the singlet oxygen mechanism proposed and rate constants for the key steps that mediate the oxidation.

Zinc phthalocyanines containing one (mono carboxy phenoxy, ZnMCPPc), four (tetra carboxy phenoxy, ZnTCPPc), and eight (tetra isophthalic acid, ZnTIPAPc) carboxyl groups were covalently conjugated to amine-functionalized glass wool (GW). The GW-Pcs were characterized and evaluated for singlet oxygen generation. The photocatalytic efficiencies of the GW-Pcs were assessed using methyl orange. Glass wool alone and the modified conjugates exhibited low to no degradation of methyl orange in the dark. The improved catalytic rate was observed for GW-ZnMCPPc and GW-ZnTCPPc compared to GW-ZnTIPAPc due to the latter's lower singlet oxygen quantum yield generation. In addition, the modified glass wool was recyclable, making it suitable candidates for future environmental applications.

The hydrogen evolution reaction depends on the accumulation of electrons on the catalytic center to enable the two-electron processes involved in water reduction. This work reports on the modification of inexpensive nickel (Ni) composite electrodes with engineered semiconductor heterojunctions based on earth-abundant transition metals that show superior hydrogen generation activity in the presence of a non-toxic electrolyte (K2CO3). This is, small amounts of cobalt (Co) or copper (Cu) oxides can improve the reactivity of composite electrodes formed by deposition of titanium (Ti) or niobium (Nb) semiconductors onto Ni surfaces. In general, modified Nb-based semiconductors show better performance and their enhanced activity can be understood in terms of modified surface potentials upon formation of semiconductor-Ni heterojunctions. Photoelectrochemical activity can be detected in the presence of Cu oxides, where hydrogen generation onset potential is reduced under UV–Vis light irradiation. The study demonstrates that small composition changes can greatly affect the activity of Nb-based Ni composite electrodes, showing exciting new applications for Nb-based materials.

Boron nitride nanotubes (BNNTs) are an emerging class of molecular container offering new functionalities and possibilities for studying molecules at the nanoscale. Herein, BNNTs are demonstrated as highly effective nanocontainers for polyoxometalate (POM) molecules. The encapsulation of POMs within BNNTs occurs spontaneously at room temperature from an aqueous solution, leading to the self-assembly of a POM@BNNT host–guest system. Analysis of the interactions between the host-nanotube and guest-molecule indicate that Lewis acid–base interactions between W=O groups of the POM (base) and B-atoms of the BNNT lattice (acid) likely play a major role in driving POM encapsulation, with photoactivated electron transfer from BNNTs to POMs in solution also contributing to the process. The transparent nature of the BNNT nanocontainer allows extensive investigation of the guest-molecules by photoluminescence, Raman, UV–vis absorption, and EPR spectroscopies. These studies revealed considerable energy and electron transfer processes between BNNTs and POMs, likely mediated via defect energy states of the BNNTs and resulting in the quenching of BNNT photoluminescence at room temperature, the emergence of new photoluminescence emissions at cryogenic temperatures (<100 K), a photochromic response, and paramagnetic signals from guest-POMs. These phenomena offer a fresh perspective on host–guest interactions at the nanoscale and open pathways for harvesting the functional properties of these hybrid systems.

Metal nanoparticles are characterized by a high surface-to-volume ratio, which significantly enhances their catalytic properties compared to the metal bulk. Despite their increased catalytic performance, they have no advantages in terms of separation when compared to homogeneous catalysts. Therefore, the use of other heterogeneous materials – e.g., inorganic metal oxides – to support metal nanoparticles and facilitate their separation and reusability has been extensively explored in the last two decades. Although the main role of these supports is to hold the particles in place, they can also play an important function in the catalytic activity of the new material. Thus, materials usually regarded as simple supports can infer other properties to the catalyst such as acidic, electrical or photochemical properties. This chapter focuses on the use of supported metal nanoparticles in catalysis, with an emphasis in photocatalysis, and describes the role that supports can play. The chapter intends to introduce the reader to the use of metal nanoparticles in the field of heterogeneous catalysis giving examples of different materials and catalytic systems. While it is not a comprehensive summary of the current literature, it provides the reader with the essential readings to acquire a basic knowledge in the field of nanocatalysis.

A single-molecule microscopy study of the interaction of dye-modified alkanes, alkenes, and alkynes with nanostructured catalysts based on TiO2 reveals significant differences in the desorption kinetics of the probe molecules depending on the chemical nature of the catalyst. A comparison of TiO2 with materials decorated with palladium (Pd@TiO2) or molybdenum/cobalt (MoCo@TiO2) reveals kinetic differences that in part justify the better performance of MoCo@TiO2 in semihydrogenation reactions. Whereas the single-molecule desorption rate is similar to 50% higher for MoCo@TiO2 than Pd@TiO2, analysis at the bench scale indicate alkene-to-alkane conversion is around 10 times faster for Pd (k(2)(Pd) = 0.02 s(-1)) than for MoCo (k(2)(MoCo) = 0.002 s(-1)) catalysts. This suggests selectivity is not solely determined by the desorption processes and that the hydrogenation rate constant (k(21)) for the on-surface hydrogenation of alkenes to alkanes is much faster for Pd@TiO2 than for MoCo@TiO2. Thus, the latter shows greater selectivity toward partial hydrogenation reactions compared with Pd@TiO2, whose great hydrogenation performance becomes a disadvantage for the selectivity needed for semihydrogenation processes.

The absence of a secure long-term sustainable energy supply is recognized as a major worldwide technological challenge. The generation of H2 through photocatalysis is an environmentally friendly alternative that can help solve the energy problem. Thus, the development of semiconductor materials that can absorb solar light is an attractive approach. TiO2 has a wide bandgap that suffers from no activity in the visible spectrum, limiting its use of solar radiation. In this research, the semiconductor absorption profile was extended into the visible region of the solar spectrum by preparing porphyrin-TiO2 (P-TiO2) composites of meso-tetra(4-bromophenyl)porphyrin (PP1) and meso-tetra(5-bromo-2-thienyl)porphyrin (PP2) and their In(III), Zn(II) and Ga(III) metal complexes. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed on the porphyrins to gain insight into their electron injection capability. The results demonstrate that P-TiO2 systems merit further in-depth study for applications that require efficient photocatalytic H2 generation.

Lignin-protected TiO2 can reduce the release of free radicals photogenerated by TiO2. This can be achieved through the intrinsic absorption of lignin that acts as an antioxidant strategically located on the surface of TiO2 particles while retaining – and to some degree improving – the light absorbing and scattering properties of TiO2. A 1–3% loading of lignin is sufficient to achieve this protection, with the coating produced photochemically taking advantage of the intrinsic free radical photogeneration capacity of TiO2. The process has been scaled up to amounts around 50 g per day by developing a large (10–25 L) flow photoreactor. As industry tends to use larger particles, our studies show that radical generation is lower with 100 nm, compared with 25 nm TiO2 particles; further, rutile is less reactive than anatase, a desirable characteristic in the fields of sunscreen, cosmetic and health applications.

A catalyst based on Pd on glass wool (Pd@GW) shows exceptional performance and durability for the reduction of nitrobenzene to aniline at room temperature and ambient pressure in aqueous solutions. The reaction is performed in a flow system and completed with 100% conversion under a variety of flow rates, 2 to 100 mLmin(-1) (normal laboratory fast flow conditions). Sodium borohydride or dihydrogen perform well as reducing agents. Scale-up of the reaction to flows of 100 mLmin(-1) also shows high conversions and robust catalytic performance. Catalyst deactivation can be readily corrected by flowing a NaBH4 solution. The catalytic system proves to be generally efficient, performing well with a range of itroaromatic compounds. The shelf life of the catalyst is excellent and its reusability after 6-8 months of storage showed the same performance as for the fresh catalyst.

The photodecomposition of azides to generate nitrenes usually requires wavelengths in the <300 nm region. In this study, we show that this reaction can be readily performed in the UVA region (368 nm) when catalyzed by Pd-decorated TiO2. In aqueous medium the reaction leads to amines, with water acting as the H source; however, in non-protic and non-nucleophilic media, such as acetonitrile, nitrenes recombine to yield azo compounds, while azirine-mediated trapping occurs in the presence of nucleophiles. The heterogeneous process facilitates catalyst separation while showing great chemoselectivity and high yields.

Versatile and recyclable heterogeneous photocatalysts based on the use of glass wool supported ruthenium complexes and organic dyes.