Haingomalala Lucette Tidahy

Noble‐Metal‐Based Catalysts Supported on Zeolites and Macro‐Mesoporous Metal Oxide Supports for the Total Oxidation of Volatile Organic Compounds

The use of porous materials to eliminate volatile organic compounds (VOCs) has proven very effective towards achieving sustainability and environmental protection goals. The activity of zeolites and macro-mesoporous metal-oxide supports in the total oxidation of VOCs has been investigated, with and without noble-metal deposition, to develop highly active catalyst systems where the formation of by-products was minimal. The first catalysts employed were zeolites, which offered a good activity in the oxidation of VOCs, but were rapidly deactivated by coke deposition. The effects of the acido-basicity and ionic exchange of these zeolites showed that a higher basicity was related to exchanged ions with lower electronegativities, resulting in better catalytic performances in the elimination of VOCs. Following on from this work, noble metals were deposited onto macro-mesoporous metal-oxide supports to form mono and bimetallic catalysts. These were then tested in the oxidation of toluene to study their catalytic performance and their deactivation process. PdAu/TiO(2) and PdAu/TiO(2) -ZrO(2) 80/20 catalysts demonstrated the best activity and life span in the oxidation of toluene and propene and offered the lowest temperatures for a 50 % conversion of VOCs and the lowest coke content after catalytic testing. Different characterization techniques were employed to explain the changes occurring in catalyst structure during the oxidation of toluene and propene.

Titanium oxide nanotubes as supports of Au or Pd nano-sized catalysts for total oxidation of VOCs

Abstract Titanium oxide nanotubes (TNTs) have been synthesized via laboratory-made TiO2 A and commercial TiO2 P25. 1.5wt% gold or palladium were deposited on TNTA and TNTP25 supports and the catalytic activity was evaluated in propene, methyl ethyl ketone (MEK) and toluene total oxidation. The catalytic properties of supported TNT were correlated with the structural peculiarity and the nature of the TNT, but also with the nature of the noble metal and the kind of the VOC.

Effects of the treatment and the mesoporosity of mesostructured TiO2 impregnated with noble metal for VOCs oxidation

Abstract Catalytic oxidation of volatile organic compounds (VOCs) was carried out over catalysts prepared from different nanostructured mesoporous TiO 2 presenting high surface areas and mesoporosity from 2.9 to 10.1 nm. These Pd impregnated solids were found to be powerful catalysts for total oxidation of toluene. However, the pore diameter of 2.9 nm, leading to palladium particles accessible and reducible in the mesopores should explain the interesting catalytic behavior of the Pd/mesoporous TiO 2 sample prepared by CTMABr surfactant and calcined at 400°C.

Characterisation of new Pd / hierarchical macro-mesoporous ZrO2, TiO2 and ZrO2-TiO2 catalysts for toluene total oxidation

Amorphous (macro)-mesoporous ZrO 2 , TiO 2 and ZrO 2 -TiO 2 have been synthesised and characterised for volatile organic compounds (VOCs) catalytic oxidation. These solids used as catalytic supports present high surface areas. The stability of the porous structure after the calcination at 400°C is observed for ZrO 2 -TiO 2 and TiO 2 but partial breakdown of the structure occurred for ZrO 2 by the crystallisation to tetragonal phase. All these Pd impregnated solids are found to be powerful catalysts for total oxidation of toluene. Pd/TiO 2 presents the highest catalytic potential. The lowest toluene adsorption enthalpy, the low coke content observed after the catalytic test and the highest pore diameter leading to palladium particles more accessible and reducible should explain the interesting catalytic behaviour of Pd/TiO 2 .

Characterisation of palladium supported on exchanged BEA and FAU zeolites for VOCs catalytic oxidation

0.5wt% palladium supported on exchanged BEA and FAU zeolites have been characterised for volatile organic compounds (VOCs) catalytic oxidation. BEA and FAU zeolites have been exchanged with different cations to study the influence of alkali metal cations (Na + , Cs + ) and H + in Pd based catalysts on propene total oxidation. Oxidation of propene depends significantly on the type of zeolites and on the compensating cation of the zeolite. According to sample, the catalytic activity is explained by the surface areas of the catalysts, the adsorption energies for VOC, the influence of the electronegativity of the compensating cation on the Pd particles, the Pd dispersion and the PdO reducibility.

H2 production by dry reforming of biogas over Ni-Co-Mg-Al mixed oxides prepared via hydrotalcite route

Ni, Co, Mg and Al mixed-oxide catalysts derived from hydrotalcite were synthesized by coprecipitation for the dry reforming of biogas. The catalysts were characterized using X-ray diffraction, Differential Scanning Calorimetry and Thermogravimetric analysis. The specific surfaces were determined by the BET method. After calcination under an air flow, hydrotalcite-like precursors were completely decomposed. The dry reforming of biogas was carried out using a mixture of CH4:CO2 (1:1) after 2 hours of reduction under an H2 flow at 800 °C. Ni-Co containing catalyst revealed better catalytic activity than the monometallic Co catalyst.

Preparation and characterization of Ni-Co-Mg-Al mixed oxides derived from layered double hydroxides and their performance in the dry reforming of methane

The hydrotalcite route was used to prepare Ni and Co oxides catalysts, with different Ni/Co contents. The catalytic performance of these oxides was investigated with the dry reforming of methane in order to produce energy vector from renewable energy. The samples were characterized, before and after calcination, by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TG), Fourier Transform Infrared spectroscopy (IR), and determination of the specific surfaces by the BET method. After calcination at 800 °C under an air flow, the hydrotalcite structure was completely decomposed. The dry reforming of methane was carried out using a mixture of CH4:CO2 (1:1) after 2 hours of reduction under an H2 flow at 800 °C. Ni-Co based catalysts revealed better catalytic activity than the Co based one.

Effect of noble metal deposition in zeolitic structures on their adsorption capacities

Experimental determination of Henry constants and adsorption heat for various VOCs on faujasite type zeolites (NaY, HY and CsY with a Si/Al ratio of 2.4) and their Palladium impregnated form were achieved by a pulse chromatographic technique from 448 to 623K for seven alkanes (linear, branched and cyclic probes) and from 523 to 673K for three aromatic compounds (toluene, m-xylene and chlorobenzene). The Henry constant increases with the cation size and decreases if the zeolite is impregnated.

Steam reforming of toluene for hydrogen production over NiMgALCe catalysts prepared via hydrotalcite route

Ni_xMg_6-xAl_1.8Ce_0.2 (with 0 ≤ x ≤ 6) mixed oxides catalysts were prepared by hydrotalcite route. All the oxides were calcined at 800°C and characterized by different physicochemical methods and their catalytic performances were tested toward steam reforming of Toluene. In the steam reforming process, reducing pretreatment is a necessary step to activate the catalyst. Ni₂Mg₄Al_1.8Ce_0.2 shows the better toluene conversion and the best performance (H₂ production) among all the catalysts.