Bernard Coq

Catalysis by hydrotalcites and related materials

Catalytic applications of Layered Double Hydroxides (LDH) or anionic clays have for a long time focused on the condensation reactions carried out with mixed oxides obtained by calcinations of Mg/Al LDH. However, the versatile character of materials prepared from these LDH exhibiting Lewis or Brønsted type basic sites has recently been underlined, and led us to contemplate extended applications in clean industrial processes. Moreover, due to their wide variety of compositions, LDH are also attractive precursors of multicomponent nanostructured catalysts. They give rise to supported metal catalysts whose metal support interaction and cooperation can be fine-tuned, as illustrated in pertinent case studies such as the hydrogenation of nitriles and the “one-pot” synthesis of methyl isobutyl ketone from acetone.

Catalytic reduction of N2O by NH3 in presence of oxygen using Fe‐exchanged zeolites

The influence of ammonia on the reduction of N2O in presence of oxygen over Fe‐zeolite has been studied. It is found that BEA zeolite is the most efficient host structure for iron ions to catalyse the reduction of N2O with NH3.

Influence of the metal function in the “one-pot” synthesis of 4-methyl-2-pentanone (methyl isobutyl ketone) from acetone over palladium supported on Mg(Al)O mixed oxides catalysts

Pd/Mg(Al)O samples (0.05 < Pd < 0.5 wt%) were evaluated in the gas phase reaction of acetone with hydrogen to methyl isobutyl ketone (MIBK). The catalysts were prepared by impregnating a calcined Mg–Al layered double hydroxide with Pd acetylacetonate in toluene solution. The highest selectivity to MIBK was achieved with ca. 0.2 wt% Pd and size of Pd particles of ca. 3–5 nm.

Layered double hydroxides: precursors for multifunctional catalysts

One-pot cascade reactions which involve multifunctional catalysts possessing different functions on the surface attract a growing interest. Relevant examples of the use of this type of catalysts in one-pot syntheses involving hydrogenation/dehydrogenation and aldol condensation reactions which give rise to valuable organic compounds are reported in this paper. It is shown that the layered double hydroxides (LDH) are precursors materials particularly adapted for the preparation of catalysts exhibiting acido/basic and redox sites. The paramount importance of the nature (Lewis or Bronsted) and the strength of the basic sites, as well as the nature of the metallic function of the supported metal catalysts obtained from LDH is discussed. It is emphasized on the equilibrium between the basic and metallic functions required to reach high activities and selectivities.

One-step sol-gel synthesis of sulfated-zirconia catalysts

Sulfated-zirconia catalysts were prepared by a one-step sol-gel method. Two different protocols were studied in which sulfuric acid is introduced either with the hydrolysis water, or in the zirconium alkoxide solution inn-propanol. After calcination at 923 K these two materials were compared with sulfated-zirconia prepared in two steps by post-sulfation of zirconium hydroxide obtained either by the sol-gel method or by precipitation of inorganic salts. The sulfated-zirconias prepared by the one-step protocol are the most active catalysts for the hydroconversion ofn-hexane. Moreover, the sample prepared by adding sulfuric acid through the hydrolysis water exhibits different textural properties and enhanced activity forn-hexane conversion. These different behaviours cannot be explained by the sulfur content.

Hydrogenation of substituted acrolein over alumina supported ruthenium catalysts

The gas phase hydrogenation of acrolein, 2-methyl-2-propenal, 2-butenal and 3-methyl-2-butenal was studied on Ru/Al2O3 and RuM/Al2O3 catalysts (M=Sn, Fe, Zn, Ge, Sb). The specific activity increases when the second element is added to the parent Ru/Al2O3 catalyst. This was ascribed to the activation of the C=O bond by Mδ+ species. Tin is the only additive which promotes the allyl alcohol selectivity. When methyl groups are tagged on the C=C bond the selectivity to the unsaturated alcohol increased sharply due to the steric hindrance against the adsorption of the substrate via the C=C double bond.

Catalytic behaviour of Cu/ZrO2 and Cu/ZrO2(SO42−) in the reduction of nitric oxide by decane in oxygen-rich atmosphere

The selective catalytic reduction (SCR) of NO by decane under an oxidising atmosphere has been carried out on Cu/ZrO2 and Cu/ZrO2(SO42−). Zirconia-supported Cu catalysts were prepared by ligand exchange with Cu acetylacetonate followed by calcination at 773 K. The solids obtained were characterised by temperature programmed reduction (TPR) by hydrogen and temperature programmed desorption (TPD) of NO. Cu/ZrO2 is active and selective in the reduction of NO by decane at low temperature (< 600 K) but oxidises NO to NO2 between 640 and 770 K. By contrast, whatever the temperature, a total selectivity to nitrogen is obtained with Cu/ZrO2(SO42−). About 40% NO conversion to N2 is observed with GHSV of 70 000 h−1. The promoting effect of sulfate is attributed to the large increase of acidity and the strong interaction between copper and sulfur species which is evidenced by TPD of NO and TPR by H2.

Infrared spectroscopy and microcalorimetry studies of CO adsorption on sulfated zirconia supported platinum catalysts

Carbon monoxide adsorption has been investigated on Pt particles supported on a high surface area zirconia and sulfated zirconias. The accessibility of the Pt surface determined from the comparison of H2 chemisorption and transmission electron microscopy depends on two parameters: the temperature of treatment in air used to dehydroxylate sulfated zirconia, and the temperature of reduction. An oxidative pretreatment at 823 K yields a poor accessibility of Pt (0.03 < H/Pt < 0.05) whatever the temperature of reduction, whereas a Pt dispersion of 0.6 can be obtained by oxidation at 673 K followed by a mild reduction at 473 K. FTIR spectroscopy of adsorbed CO on Pt/ZrO2 shows besides the normal linear species at 2065 cm−1, a band at 1650 cm−1 which is attributed to CO bridged between Pt and Zr atoms. On Pt/ZrO2-SO42−, all bridged species tend to disappear, as well as the dipole-dipole coupling andvCO is shifted by 57 cm−1 to higher frequencies. These results are attributed to sulfur adsorption on Pt which decreases the electron back-donation from Pt to the 2π* antibonding orbital of CO. The lower initial heat of CO adsorption observed on Pt/ZrO2-SO4/2− supports this proposal.

Influence of operating protocol in the temperature-programmed reaction of NO with decane on Cu/mordenite

A Cu/mordenite catalyst was prepared by ion exchange and characterized by N2 Sorption, XRD, TPR by H2 and TPD by NO. The catalyst was evaluated in the selective catalytic reduction of NO by decane in O2-rich atmosphere under temperature-programmed reaction from 293 to 773 K. Two NO reduction profiles at 590 and 650 K occur under these conditions. By testing different operating protocols and different alkanes as reductants, it was concluded that the low temperature peak (590 K) is due to alkane condensed in the porosity of mordenite.

KMg1−xPdxF3 with Perovskite-Like Structures as Precursors for the Catalytic Hydroconversion of CCl2F2 and CHClF2

Several fluoride type perovskites, with formula KMg1−xPdxF3, have been prepared for the first time. The enlargement of their cell parameters has been associated with the insertion of Pd into the structure. After reduction, these new compounds, when tested in the hydrodechlorination reaction of CCl2F2 and CHClF2, showed higher selectivities to CHClF2 and CH2F2, respectively, than other Pd catalysts supported on KMgF3.