Preparation of ecological catalysts derived from Zn hyperaccumulating plants and their catalytic activity in Diels–Alder reaction

Zn hyperaccumulating plants Noccaea caerulescens and Anthyllis vulneraria were used as the starting material for preparation of novel Lewis ecological catalysts. Those catalysts efficiently mediate the Diels–Alder reaction. High yields, very good regio- and diastereoselectivity, low catalyst loading and the possibly of its recovery and reuse, along with mild reaction conditions, eco-friendly treatment and short reaction time, are the key advantages of the presented approach.     

Influence of the formulation of catalysts deposited on cordierite monoliths for acetic acid oxidation

Monolithic catalysts are prepared by washcoating cordierite monoliths with different sols (Pt/Al₂O₃, Pt/CeO₂, Pt/ZrO₂, Pt/Al₂O₃CeO₂, Pt/Al₂O₃ZrO₂, and Pt/CeO₂ZrO₂). These sols are prepared by a sol–gel process and characterized by specific surface area (S_BET), inductively coupled plasma, hydrogen chemisorption, high-resolution transmission electron microscopy, field emission scanning electron microscopy, oxygen storage capacity, X-ray diffraction, temperature-programmed reduction, CO₂ chemisorption, and the model reaction of 3,3-dimethylbutene isomerization. The catalytic performances of the monolithic catalysts are then evaluated for the acetic acid oxidation. The nature of catalyst coating has been found to influence the adherence with the cordierite monolith and the presence of cerium in the catalyst appears to increase the adherence of the latter. Pt/CeO₂, Pt/Al₂O₃CeO₂, and Pt/CeO₂ZrO₂ are found to be the most reducible catalysts (oxygen storage capacity and temperature-programmed reduction) and to have the lowest acidities (3,3-dimethylbutene isomerization). CO₂ chemisorption shows that these catalysts possess a good basicity. From the relation established between the catalytic activity and the redox and acid–base properties it has been concluded that the reducibility is the key factor for a good catalytic activity although the basicity has a significant influence on the catalytic performance.     

Degradation of VOCs and NOx over Mg(Cu)–AlFe mixed oxides derived from hydrotalcite-like compounds

A series of Mg(Cu)–AlFe mixed oxides derived from hydrotalcite-like compounds has been prepared. These solids were characterized by various physicochemical methods and their catalytic performances were tested towards the catalytic oxidation of propene and the simultaneous elimination of propene and NO_x. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the formation of the hydrotalcite structure for all the solids, except for Cu₄AlFe HT, for which a mixture of the hydrotalcite and the malachite phases is observed. The XRD study of the calcined samples revealed the existence of metal oxides and spinels of types MgO, CuO,

-Fe₂O₃ or/and Fe₃O₄, MgFe₂O₄ and CuFe₂O₄. During propene oxidation, it was shown that the increase in the copper content enhanced the activity of the solids. However, Cu₂Mg₂AlFe 500, with the highest amount of surface copper species, exhibited the best activity towards the simultaneous elimination of propene and NO. Indeed surface Cu species are the active sites, while bulk Cu species could provide the adsorption sites for nitrogen species.     

Solvent-free epoxidation of himachalenes and their derivatives by TBHP using [MoO2(SAP)]2 as a catalyst

Himachalenes, sesquiterpenes isolated from the essential oil of Cedrus atlantica, are abundant and relatively inexpensive natural molecules of high interest, of which classical chemical transformations have enlarged the application potential. Solvent-free epoxidation using aqueous TBHP as an oxidant and [MoO₂(SAP)]₂ as a catalyst is performed herein for the first time with this family of natural compounds and with related halogenated derivatives.     

Modification of the catalytic properties of palladium by rare earth (La, Ce) addition: Catalytic activity and selectivity in hydrocarbon conversion

Pd/Al₂O₃ catalysts modified by cerium or lanthanum promoters are tested for hydrocarbon conversion: methylcyclopentane (MCP) hydrogenolysis, 2-methylpentane (2MP) isomerization and 3-methylhexane (3MH) hydrocracking, deshydrocyclization and aromatization. The following parameters are reviewed: (i) precursor salt of palladium (chloride or nitrate), (ii) rare earth nature (La or Ce), (iii) rare earth content within the range 0–100% and (iv) impregnation mode (coimpregnation or successive impregnations). The influence of chloride coming from the precursor salt of palladium on the catalytic behaviour is strongly underlined. Chlorine anions are trapped by rare earth cations at the interface, as evidenced in a subsequent paper dealing with characterization studies of these same catalysts (K. Kili, L. Hilaire, F. Le Normand, submitted). Although the reactions readily occur on metallic sites, as evidenced by ¹³C labelled experiments, the addition of rare earth increases the activity and modifies the selectivity, especially for 2MP isomerization. These changes are rationalized in terms of significant modification of the kinetic surface parameters (competitive hydrogen and hydrocarbon coverages). This is explained by (i) lowering of the hydrogen coverage of the palladium sites accompanying surface diffusion on the interface with the support and (ii) creation of new selective sites at the transition metal–rare earth interface. The other parameters investigated yield only minor changes of the catalytic behaviour.     

Coordination compounds from the planar tridentate Schiff-base ligand 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol (mqmpH) with several transition metal ions: Use of [Fe(mqmp)(CH3OH)Cl2] in the catalytic oxidation of alkanes and alkenes

Four coordination compounds were synthesized in high yields from different transition metal ions (Fe^III, Co^II, and Cu^II) and an in situ generated Schiff-base ligand, i.e. 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol (mqmpH). The compounds were characterized by single-crystal X-ray diffraction, ESI-MS, IR spectroscopy, and ligand-field spectroscopy. The iron(III) complex is an efficient catalyst for the oxidation of alkanes and alkenes, under relatively mild conditions and with dihydrogen peroxide as terminal oxidant.