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The salen complex catalyst (SAA) in combination with Bu4NBr as co-catalyst shows high catalytic activity in reactions of epoxides (I) and (IV) with carbon dioxide to give the corresponding carbonates.

Heteroatoms in zeolites provide them their catalytic activity. The silicon atom is always tetrahedrally coordinated and its valence IV, those of the heteroatoms much more varied. This is further complicated by the easy removal of heteroatoms out of the zeolite framework forming extra-framework phases. The change in coordination and removal of the framework atoms is often paralleled with enhanced catalytic performance and thus the precise characterization of heteroatoms in zeolites, as a function of synthesis and post-synthesis treatments, is topic of much research. In this review we summarize structural characterization of various heteroatoms using X-ray absorption spectroscopy. This method is in particular suitable, because it is element-specific, can be used to determine structure of amorphous samples, and can be applied under pretreatment and catalytic conditions. Aluminum shows a rich variation in coordination and, depending on the conditions, such as temperature and, notably, water content, zeolitic aluminum can be three, four, five and six-coordinate. The Bronsted acid site is associated with a strongly distorted tetrahedral coordination of the framework aluminum. During activation and along catalytic reactions, there is a large variation in the distortion of the local environment of aluminum, and the flexibility of the zeolite framework to accommodate such structural differences is essential to guarantee a long life time of the material as working catalyst. Iron in the zeolite framework is easily removed. The extra-framework iron species are extensively characterized, however, no consensus about their structure has been reached. Framework iron is Fe 3+ , extra-framework iron mostly Fe 2+ . The coordination of other tri- and tetravalent heteroatoms, such as gallium, boron, titanium, germanium, and tin are less investigated. It is however obvious that their structure is a function of the conditions the zeolite is exposed to. Like aluminum, the titanium atom easily switches coordination in a reversible way. All hetero-atoms often form extra-framework species. This review identifies the importance of changes in local structure of heteroatoms and the easy removal of these hetero-atoms from the framework. Often it is the extra-framework species that is responsible for catalytic activity.

Review: use of vibrational and electronic spectroscopies in the characterization of meallorganic materials, such as metal organic frameworks (MOFs); 194 refs.

The large unit cells, the enormous flexibility and variation in structural motifs of MOFs represent a big challenge in the characterization of MOF materials, particularly in cases where single crystal diffraction data are not available. In this critical review it is shown that in cases where only powder diffraction data are available additional structural information, particularly regarding local coordination within the inorganic cluster, are often mandatory in order to solve the structure. There are also cases where the inorganic cluster does not follow the symmetry of the overall structure. In such cases diffraction techniques will just “see” an average structure, missing the local structure: a lack that may be critical for understanding the specific properties of the material. In both cases, EXAFS spectroscopy is the tool that provides complementary structural information on the inorganic cluster and the way it binds to the ligand. Selected examples will show how EXAFS will be relevant in: (i) confirming the structure obtained from diffraction refinements; (ii) highlighting that the inorganic cornerstone has a lower symmetry with respect to that of the organic framework; (iii) obtaining the local structure of the inorganic cluster in the desolvated material when desolvation causes a partial loss of long range order; (iv) obtaining the local structure of the inorganic cluster in the desolvated material after coordination of a probe (or reactant) molecule, including cluster deformation upon molecule coordination and metal–molecule binding distance; (v) evidencing the presence of impurities in the form of amorphous extra-phases (339 references).

This critical review describes the reactivity of heterogeneous catalysts from the point of view of four simple, but essential for Chemistry, molecules (namely dihydrogen, carbon monoxide, nitrogen monoxide and ethylene) that are considered as probes or as reactants in combination with “in situ” controlled temperature and pressure Infrared spectroscopy. The fundamental properties of H2, CO, NO and C2H4 are shortly described in order to justify their different behaviour in respect of isolated sites in different environments, extended surfaces, clusters, crystalline or amorphous materials. The description is given by considering some “key studies” and trying to evidence similarities and differences among surfaces and probes (572 references).

Knowledge of the structure of catalysts is essential to understand their behavior, which further facilitates development of an active, selective, and stable catalyst. Determining the structure of a functioning catalyst is essential in this regard. The structure of a catalyst is prone to change during the catalytic process and needs to be determined in its working conditions. In this tutorial review, we have summarized studies done at synchrotron radiation facilities that illustrate the capability to determine catalyst structure using X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES). These studies aim at facilitating the determination of the dynamic structure-performance relationships during a catalytic process.

Two preparations of tetragonal zirconia (t-ZrO2) stabilized with 3 mol% Y2O3 have been characterized, and their features compared with those of a 2 mol% t-ZrO2 preparation and of a monoclinic zirconia (m-ZrO2) preparation.At ambient temperature, CO adsorption occurs only on surface cationic Lewis acid sites located in crystallographically defective configurations. The various t-ZrO2 preparations present several types of such defective sites, depending on the temperature of the sintering stage. The spectral features of the ambient-temperature interaction of t-ZrO2 with CO are complemented, on quantitative grounds, by gas-volumetric and microcalorimetric data. At high firing temperatures, amorphous phases start segregating from the t-ZrO2 crystallites, causing the ambient-temperature adsorptive capacity towards CO to decline.Upon CO adsorption at low temperaure (ca. 77 K), weaker adspecies form prevalently. These are ascribed to CO adsorption on cationic Lewis acid sites located in regular patches of low-index crystal planes, and to CO H-bonded to surface OH groups.Different t-ZrO2 preparations and differently sintered samples exhibit different particle sizes and various proportions of crystal surface defect sites vs. regular-face terminations: these differences are reliably monitored by CO adsorption patterns observed via IR spectroscopy, both at 300 and ca. 77 K.

TS-1 and Fe-MFI systems have been chosen as cases studies for describing the behavior of single-site catalysts. We will report a concise review of the firmly established knowledge and of the open problems concerning the structure and the reactivity of Ti and Fe sites in TS-1 and Fe-MFI in partial oxidation catalysts. Some new experimental and theoretical results will also be described.

Palladium complexes supported by tridentate phosphido diphosphine ligands (P(o-C6H4PR2)2: 1, R = iPr; 2, R = Ph) have been synthesized, characterized, and tested as catalysts for the electrophilic allylation of aldehydes. The palladium complex 2 resulted in an interesting catalyst for electrophilic allylation in the presence of allyltributyltin, giving good yields under very mild reaction conditions and even in the absence of the solvent.

Room-temperature ionic liquids (ILs) are a class of novel green chemicals being designed to replace traditional volatile organic solvents in industrial processes. The potential effects of ILs on aquatic ecosystems have been poorly studied, despite the possibility of unintentional discharge into rivers and lakes, and their intentional disposal in wastewater treatment plants. We studied the effects of three imidazolium ionic liquids, 1-butyl-, 1-hexyl- and 1-octyl-3-methylimidazolium bromide, on the growth rates of two freshwater algae, Scenedesmus quadricauda and Chlamydomonas reinhardtii, in 96 h standard toxicity bioassays. Increases in alkyl chain length increased the toxicity of these ionic liquids to both S. quadricauda (EC50 values of 0.005–13.23 mg L–1) and C. reinhardtii (EC50 values of 4.07–2138 mg L–1). Bioassays were performed in both nutrient-amended media and low-nutrient groundwater to evaluate if test conditions altered IL toxicity. EC50 values for S. quadricauda were similar between nutrient media and groundwater for all ILs tested, while the presence of nutrient media appeared to partially mitigate the toxicity of ILs to C. reinhardtii (groundwater EC50 < media EC50). Overall, S. quadricauda was much more sensitive than C. reinhardtii to all ILs tested, perhaps reflecting differences in cell wall structure. EC50 values suggest that ILs are more, or just as, toxic to algae than many of the solvents they are intended to replace. Results of this study show that ionic liquids can elicit a range of algal responses, suggesting that a diversity of target organisms be tested in order to predict the effects of ILs in natural environments.

A full understanding of a catalytic reaction requires a thorough identification of precursor and intermediate species. In this regard spectroscopies, in general, and infrared (IR) spectroscopy, in particular, can play an important role. However, the spectroscopic identification of precursor and intermediate species is often difficult owing to their transient nature. In this review we show how control of experimental parameters such as temperature, equilibrium pressure, and reactant–catalyst contact time allows experimentalists to alter the rates of dynamic processes and consequently to modify appreciably the relative concentrations of precursor, intermediate, and product species present under reaction conditions. In this context, time-resolved FTIR spectroscopy (with constant temperature and pressure during the experiment) and also temperature-time resolved (with both temperature and time changing simultaneously in a controlled way during the experiment) can be useful for kinetic investigations of several types of reactions. In this review several examples demonstrating the potential value of FTIR spectroscopy for the identification of surface transient species are discussed. These are classified in four main categories: (i) adsorption processes and transformations in the adsorbed state; (ii) proton-catalyzed oligomerization and polymerization of alkenes and unsaturated molecules in protonic zeolites; (iii) oligomerization reactions catalyzed by basic surface sites, and (iv) oligomerization and polymerization of alkenes on catalysts incorporating supported transition metal ions. All these reactions are discussed in the framework of a few common potential energy profiles in which the evolution from the precursor through the intermediate species to the final products is governed by the relative height of the corresponding activation energy barriers.

A titanium binaphthyl-bridged Schiff base complex proved to be an efficient catalyst for the hydrogen peroxide oxidation of aromatic and aliphatic sulfides to the corresponding sulfoxides in satisfactory yields under solvent-free conditions.