The current established catalytic processes used in chemical industries use metals, in many cases precious metals, or metal oxides as catalysts. These are often energy-consuming and not highly selective, wasting resources and producing greenhouse gases. Metal-free heterogeneous catalysis using carbon or carbon nitride is an interesting alternative to some current industrialized chemical processes. Carbon and carbon nitride combine environmental acceptability with inexhaustible resources and allow a favorable management of energy with good thermal conductivity. Owing to lower reaction temperatures and increased selectivity, these catalysts could be candidates for green chemistry with low emission and an efficient use of the chemical feedstock. This Review highlights some recent promising activities and developments in heterogeneous catalysis using only carbon and carbon nitride as catalysts. The state-of-the-art and future challenges of metal-free heterogeneous catalysis are also discussed.

We present results from a diffusion study of polymer chains in thin films, in which the mobility of chains labeled with a fluorescent dye in a matrix of unlabeled chains has been measured using fluorescence recovery after patterned photobleaching. The results presented here indicate that there is a substantial decrease in the lateral diffusion coefficient for films thinner than ∼1500 Å.

Boron makes it selective: Carbon nanotubes (CNTs) modified by boron oxide catalyze the oxidative dehydrogenation of propane to propene with remarkable selectivity. Nanocarbon can be an attractive alternative to conventional metal oxides, as it enables a feasible investigation of the reaction mechanism and provides a sustainable technology for alkane conversion

Constant CO(x)-free H2 production from the catalytic decomposition of ammonia could be achieved over a high-surface-area molybdenum carbide catalyst prepared by a temperature-programmed reduction-carburization method. The fresh and used catalyst was characterized by N2 adsorption/desorption, powder X-ray diffraction, scanning and transmission electron microscopy, and electron energy-loss spectroscopy at different stages. Observed deactivation (in the first 15 h) of the high-surface-area carbide during the reaction was ascribed to considerable reduction of the specific surface area due to nitridation of the carbide under the reaction conditions. Theoretical calculations confirm that the N atoms tend to occupy subsurface sites, leading to the formation of nitride under an NH3 atmosphere. The relatively high rate of reaction (30 mmol/((g of cat.) min)) observed for the catalytic decomposition of NH3 is ascribed to highly energetic sites (twin boundaries, stacking faults, steps, and defects) which are observed in both the molybdenum carbide and nitride samples. The prevalence of such sites in the as-synthesized material results in a much higher H2 production rate in comparison with that for previously reported Mo-based catalysts.

Steam reforming of methanol (SRM) was investigated over copper-containing catalysts supported on four different oxides and mixed oxides: Cu/ZnO/Al 2 O 3 , Cu/ZrO 2 /CeO 2 , Cu/SiO 2 and Cu/Cr 2 O 3 /Fe 2 O 3 . After observing slight differences in the way of catalyst aging and experimental exclusion of mass transport limitation effects, a detailed kinetic study was carried out at 493 K. The dependence of the reaction rate on the molar ratio of methanol and water was determined as well as the influence of addition of inert nitrogen and the main reaction products hydrogen and carbon dioxide to the reactant mixture. Although there were remarkable differences in the catalytic activity of the samples, the main mechanistic steps reflected in the rate law appeared to be similar for all catalysts. The reaction rate is mainly determined by the methanol partial pressure, whereas water is not involved in the rate determining step, except over Cu/Cr 2 O 3 /Fe 2 O 3 , where several differences in the chemistry were observed. Hydrogen and carbon dioxide were found to inhibit the reaction. These results were confirmed by a DRIFTS study at 493 K using an equimolar reactant mixture and an excess of 4:1 of water and methanol, respectively. The same surface species could be identified on each catalyst but neither kinetic modelling nor the DRIFTS spectra could give a clear answer if the reaction pathway occurs via a dioxomethylene or a methyl formate species as intermediate. Similar activation energies of SRM confirm the assumption, that the surface chemistry of SRM over copper-based systems is independent of the catalyst support material.

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The influence of the support material of low loaded (< 2 V nm -²) vanadia catalysts on selectivities, activation energies and turn over frequencies in the oxidative dehydrogenation of propane and the combustion of propene was investigated. CeO 2 , TiO 2 , Al 2 O 3 , ZrO 2 and SiO 2 supported catalysts were prepared by saturation wetness impregnation in toluene. Characterization with temperature programmed reduction and Raman spectroscopy revealed a high dispersion of surface vanadia species for all investigated catalysts. The impact of heat and mass transfer limitations on the catalytic performance has been thoroughly excluded. Selectivities towards propene as well as activation energies strongly depend on the support material. For all catalysts, propene selectivity increases with temperature. Deconvolution of the reaction network of ODP into decoupled reactions of different reactants for at least three of the catalysts is not possible, because of a significant impact of the oxidation state of the catalyst on the reaction. Except for the CeO 2 supported catalyst, the contribution of the bare support material on the activity can be neglected.

As-synthesized malic acid carbon dots are found to possess photoblinking properties that are outstanding and superior compared to those of conventional dyes. Considering their excellent biocompatibility, malic acid carbon dots are suitable for super-resolution fluorescence localization microscopy under a variety of conditions, as we demonstrate in fixed and live trout gill epithelial cells. In addition, during imaging experiments, the so-called "excitation wavelength-dependent" emission was not observed for individual as-made malic acid carbon dots, which motivated us to develop a time-saving and high-throughput separation technique to isolate malic acid carbon dots into fractions of different particle size distributions using C reversed-phase silica gel column chromatography. This post-treatment allowed us to determine how particle size distribution influences the optical properties of malic acid carbon dot fractions, that is, optical band gap energies and photoluminescence behaviors.