The physico-chemical properties of a series of Ni,Mg,Al-HTLC with Al/(Al+Mg+Ni) = 0.25 and low Ni/Mg ratios were studied by means of X-ray diffraction (XRD), thermogravimetric (TGA) and thermodifferential (DTA) analysis, N2 physissorption and temperature programmed reduction (TPR). The as-synthesized materials were well-crystallized, with XRD patterns typical of the HTLCs in carbonate form. Upon calcination and dehydration the dehydroxilation of the layers with concurrent decomposition of carbonate anions produced mixed oxides with high surface area. XRD analysis indicated that the different nickel and aluminum oxides species are well-dispersed in a poor-crystallized MgO periclase-type phase. As observed by TPR, the different Ni species showed distinct interactions with Mg(Al)O phase, which were influenced by both nickel content and calcination temperature. Regardless of the the nickel content, the reduction of nickel species was not complete as indicated by the presence of metallic dispersions
This work aims at studying the effect of CO 2 addition in the non-oxidative conversion of methane over a Mo-containing MCM-22 zeolite. Catalyst characterization made use of X-ray fluorescence, textural analysis, X-ray diffraction and diffuse reflectance spectroscopy. Molybdenum was present as highly condensed species with octahedral coordination, such as (Mo 7 O 24 ) 6 and MoO 3 species. Catalytic tests were carried out at atmospheric pressure and 700°C, with WHSV of 90g CH4 AE g Mo )1 h )1 . Coke species were studied by thermogravimetric analysis and thermoprogrammed oxidation. Besides the carbidic carbon, two other types of coke were observed: one associated to molybdenum and the other associated to Bro¨nsted acid sites located both on the catalyst surface and inside zeolite pores. The species associated to acid sites, known to be responsible for polyaromatics formation and catalyst deactivation, were reduced in a more significant way by the use of CO 2 , increasing the catalyst stability.
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