Influence of acid–base properties of cobalt–molybdenum catalysts supported on magnesium orthophosphates in isomerization of 3,3-dimethylbut-1-ene

AbstractSynthesis and physico-chemical characterization of a pure magnesium phosphate (MgP) prepared by coprecipitation, and MgP modified by introduction of cobalt–molybdenum (4–12wt.% of MoO3 with the Co/Mo ratio fixed at 0.5) have been carried out. The structural properties of these catalysts were characterized by X-ray diffraction, their textural properties were determined by N2 adsorption–desorption isotherms and the dispersion of cobalt–molybdenum was studied by XPS spectroscopy. Their acid properties have been investigated by in situ FT-IR spectroscopy of adsorbed molecules, often, 2,6-dimethylpyridine (pKa=6.7), pyridine (pKa=5.3). Co–Mo incorporation leads to a modification in the MgP acid–base properties, especially on the acid sites type and number. Thus, lower loading of cobalt–molybdenum species decreased the number of strong Lewis acid sites whereas higher loading increased it. It was found that Lewis acid sites on magnesium phosphates play an important role in the isomerization of 3,3-dimethylbut-1-ene.The 3,3-dimethylbut-1-ene (33DMB1) conversion increases with the reaction temperature from 493 to 653K for MgP, but decreases after 573K for MgP supported by Co–Mo. A linear relationship between both types of acid sites and conversion values was found. The deactivation of the catalysts appears at high reaction temperature (>573K)

Oscillatory behavior of Pd-Au catalysts in toluene total oxidation

In this work, the activity of bimetallic Pd-Au doped hierarchically structured titania catalysts has been investigated in the total oxidation of toluene. In earlier works, doping titania with group Vb metal oxides ensured an increased catalytic performance in the elimination of VOC molecules. A synergy between gold and palladium loaded at the surface of titania supports provided better performances in VOC oxidation reactions. Therefore, the main focus in this work was to investigate the durability of the prepared catalysts under long time-on-stream periods. Vanadium-doped catalysts showed a stable activity throughout the whole 110 h test, whereas, surprisingly, niobium-doped catalysts presented a cycle-like activity while nevertheless maintaining a high performance in toluene elimination. Operando Diffuse Reflectance Infrared Fourrier Transform spectroscopy (DRIFT) experiments revealed that variations in the presence of OH radicals and the presence of carbonaceous compounds adsorbed at the surface of spent catalysts varies with the occurrence of oscillations. X-ray Photoelectron Spectroscopy (XPS) results show that interactions between the material and the active phase provided extra amounts of mobile oxygen species and participated in easing the reduction of palladium. An enhanced redox reaction scheme is thus obtained and allows the occurrence of the cyclic-like performance of the catalyst

NEW INSIGHT IN THE PREPARATION OF ALUMINA SUPPORTED HYDROTREATMENT OXIDIC PRECURSORS: A MOLECULAR APPROACH

The science on the preparation of the hydrodesulfurization oxidic precursors is coming of age, but the chemistry governing their preparation is not yet clearly understood. In this paper, the chemistry of alumina supported oxomolybdate preparation is revisited taking into account the dissolution/precipitation concept recently developed. Classical preparations with the ammonium heptamolybdate and Co nitrate salts will firstly be discussed. Then the use of new starting materials for the preparation of the impregnating solutions will be considered, showing that at high Mo loading the dispersion is strongly dependant on the nature of the starting salts. The use of phosphomolybdate cobalt salts will also be considered. Lastly we will discuss the improvement of the Co promoting effect using molybdocobaltate heteropolyanions as starting materials and complexing agents. This study shows that the maturation step is the determining step for the improvement of preparation of these alumina based oxidic precursor. I

First in situ temperature quantification of CoMoS species upon gas sulfidation enabled by new insight on cobalt sulfide formation

International audienceInsights into the cobalt sulfide formation upon sulfidation (10% H2S/H2) of cobalt-based materials with 4 wt % CoO supported on alumina or silica were obtained by Quick-X-ray absorption spectroscopy monitoring analysed by multivariate curve regression analysis. A common pathway is evidenced involving the formation of supported defective CoS2 species transformed around 200-250°C into supported Co9S8 species. Upon cooling down under sulfiding atmosphere, a reverse transition towards CoS2 was observed by XAS multivariate analysis and supported by Raman analysis. This reverse transition is sensitive to the Co9S8 crystallite size: the smaller the Co9S8 nanoparticles the higher the amount of formed CoS2 after cooling. The knowledge gained on the sulfidation of monometallic cobalt-based catalysts has been used in order to isolate the X-ray absorption spectrum of the CoMoS active species formed during the sulfidation of a calcined cobalt-promoted HDS catalyst. The evolution of the concentration of the CoMoS species upon temperature increase is determined for the first time, together with those of the pristine oxidic CoMo catalyst and CoS2 and Co9S8 supported species. Although the conversion of Co9S8 into CoS2 is still observed for the HDS catalyst when temperature is decreased under H2S/H2 atmosphere, no change of the CoMoS percentage is evidenced

High resolution NMR unraveling Cu substitution of Mg in hydrotalcitesethanol reactivity

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Sulfur compounds reactivity in the ODS of model and real feeds on W-SBA based catalysts

International audienceW based catalysts were synthesized by dry impregnation of SBA-15 mesoporous silica with phosphotungstic acid (HPW) solution with W contents between 5 and 20%, the HPW compound being preserved after calcination. The catalysts performance and the reactivity of various sulfide compounds were evaluated in the oxidative desulfurization (ODS) of model solutions and of real diesels, with sulfur contents ranging from 50 to 2000 ppm. The reactivity of benzothiophene and dibenzothiophene compounds was different in the ODS of model solutions but globally identical in the ODS of SRGO. The monitoring of the concentration of a range of alkyl DBT compounds (with alkyl groups from C2 to C5) in LGO confirmed the importance of the steric hindrance of alkyl substituents in the 4,6 position near the S atom, as well as of the size of the alkyl groups. Among the xW/SBA series, the catalyst with the highest loading showed the best performance in the ODS of LGO and SRGO while the catalysts efficiency could not be discriminated in the ODS of model solutions. In the ODS of both model solutions and real feeds, the W/SBA catalyst was found to be much more efficient than a catalyst obtained by impregnation of a commercial silica with similar loading, highlighting the beneficial use of a mesoporous support with high surface area and pore volume that allowed well-dispersed tungsten species to be obtained. The quantity of sulfones precipitated and/or retained on the catalyst depended on the feed and was found to be higher in the ODS of model solution than in the ODS of real feeds. The precipitated/retained sulfones on the support may induce catalyst deactivation, which highlights the importance of the textural properties of the support. This detailed study points out the difficulty of extrapolating results obtained in the ODS of model solution to the ODS of real feeds

Increase of the Ni/W ratio in heteropolyanions based NiW hydrocracking catalysts with improved catalytic performances

In the present work, we investigated the influence of the increase ofNi/W ratio by the addition of nickel nitrate on heteropolycompound (HPC) based catalysts. Synthesized catalysts were characterized by Raman, XPS and HRTEM techniques and were examined in the model reaction of toluene hydrogenation. The Ni2SiW12O40based catalyst with a ratio of 0.36 obtained by addition of nickel nitrate was found to have the best catalytic activity compared to the most efficient of the HPC based catalysts with a stoichiometric Ni/W ratio of 0.36. Raman spectroscopy showed that the SiW12O404-HPA was decomposed during the drying step in SiW11O398-species