Eva Sarkadi-Priboczki

A Novel Radioisotope Method for Studying Catalytic Transformations over Alumina, H-ZSM-5 and H-Beta Zeolite Catalysts: Investigation of Conversion of 11C-Labeled Methanol to 11C-Labeled Dimethyl Ether and Hydrocarbons

A novel radiochemical method for investigating the catalytic transformations of the 11C-radioisotope labeled methanol over H-ZSM-5 and H-Beta zeolite catalysts has been introduced. The catalysis process was monitored by gamma detectors and the 11C-labeled products were analyzed by radio-gas chromatography. The medium pore H-ZSM-5 and H-Beta zeolite catalysts were synthesized and characterized using X-ray powder diffraction, scanning electron microscope, nitrogen adsorption, X-ray fluorescency and FTIR spectroscopy. The investigations of 11C-labeled product distributions and reaction mechanism of the conversion of [11C]methanol over H-ZSM-5 and H-Beta zeolite catalysts have been elaborated in terms of structure and acidity of the catalysts. In microreactors the effect of natural carbon compounds from environment can be a disturbing effect for the detection of inactive carbon products. Applied radio detection method eliminates these disturbing effects and detects only 11C-labeled compounds during the whole catalytic process. In the study of the transformations of carbon compounds, besides the well known 14C tracer technique and 13C MAS NMR spectroscopy investigation, the 11C-method is a new, more sensitive and simple one to monitor the transformation of the starting 11C-labeled compound by radio detectors (gamma detector) and for analyzing the 11C-labeled products by radio-gas chromatography.

Probing the influence of SSZ-13 Zeolite pore hierarchy in MTO catalysis by NASCA microscopy and positron emission profiling

An understanding of the role of the hierarchical pore architecture of SSZ‐13 zeolites on the catalytic performance in the methanol‐to‐olefins (MTO) reaction is crucial to guide the design of better catalysts. We investigated the influence of the space velocity on the performance of a microporous SSZ‐13 zeolite and several hierarchically structured SSZ‐13 zeolites. Single catalytic turnovers, as recorded by nanometer accuracy by using stochastic chemical reactions (NASCA) fluorescence microscopy verified that the hierarchical zeolites contain pores larger than the 0.38 nm apertures native to SSZ‐13 zeolite. The amount of fluorescent events correlated well with the additional pore volume available because of the hierarchical structuring of the zeolite. Positron emission tomography (PET) using 11C‐labeled methanol was used to map the 2 D spatial distribution of the deposits formed during the MTO reaction in the catalyst bed. We used PET imaging to demonstrate that hierarchical structuring not only improves the utilization of the available microporous cages of SSZ‐13 but also that the aromatic hydrocarbon pool species are involved in more turnovers before they condense into larger multiring structures that deactivate the catalyst.

Nanostructured copper, chromium, and tin oxide multicomponent materials as catalysts for methanol decomposition: 11C-radiolabeling study

Copper and chromium modified tin oxide nanocomposites were obtained via incipient wetness impregnation of high surface area nanosized SnO(2) with the corresponding metal acetylacetonates and their further decomposition in air. Powder X-ray diffraction (XRD), Nitrogen physisorption, UV-Vis, and Temperature-programmed reduction (TPR) with hydrogen were applied for the samples characterization. The catalytic activity of the obtained materials was tested in methanol conversion. A new approach based on the selective coverage of the surface with (11)C-methanol was used for the characterization of the catalytic sites. It was demonstrated that the products distribution could be controlled by the surface coverage with methanol and the role of different active sites was discussed. The modification of SnO(2) with copper oxide increased the activity in methanol decomposition to CO(2)via dioxymethylene intermediates, but the catalyst suffered considerable loss of activity due to the reduction transformations by the reaction medium and formation of an inactive intermetallic alloy. The modification with chromium changed the acid-basic properties of SnO(2) by the formation of Cr(2)O(3) nanoparticles as well as anchored to the support chromate species. The former particles facilitated the formation of dimethyl ether (DME), while the latter species converted methanol predominantly to hydrocarbons. The fraction of chromate species increased in Cu-Cr-Sn oxide multicomponent nanocomposites and promoted the formation of hydrocarbons over DME at low temperatures, while at higher temperatures, the activity of the copper species leading to CO(2) formation was more pronounced.

11C-Radiolabeling study of methanol decomposition on chromium modified SBA-15 silica

Chromium modified mesoporous SBA-15 silica was prepared by incipient wetness impregnation of the silica support with toluene solution of chromium acetylacetonate. Powder X-ray diffraction, Nitrogen physisorption, FTIR, UV–Vis and XPS techniques as well as temperature programmed reduction with hydrogen were used for the characterization of the obtained materials. The catalytic behaviour of the samples was tested in methanol decomposition to CO and hydrogen. Novel catalytic radio isotopic based method was applied for the elucidation of the role of different chromium surface species in the catalytic process. This approach is based on the selective coverage of the surface active sites with 11C- and 12C-methanol and simultaneous observation of the products of their conversion. It was found that the supported active phase represents a complex mixture of chromium oxide nanoparticles (mainly Cr2O3, CrO3) and anchored to the silica surface mono- and polychromate structures. It was established that these species differ significantly in their catalytic behavior during the methanol decomposition and the reaction mechanism of the formation of different products was discussed.

Radioactive 11C-methyl labeling for study of methanol co-reaction with methyl iodide on Fe-Beta zeolite

Abstract The 11 C-radioisotope is used to label either methanol or methyl iodide for distinction of individual methyl group in their co-reaction on Fe-H-Beta-300 zeolite. The adsorption and desorption of 11 -labeled compounds and its derivates on catalyst were followed-up by radiodetectors. The gas chromatograph FID detector on-line with a flow radioactivity detector was used to determine the origin of methyl groups in the co-reaction. The results present dimethyl ether and some hydrocarbons as co-products over light acid sites of Fe-H-Beta-300. Moreover, the radio-GC analysis confirms that, using 11 C-methanol co-reaction with methyl iodide, a newly formed radioactive compound, i.e. 11 -methyl iodide was radiodetected from 11 C-methyl fragment of methanol. This methyl exchange, as a co-reaction of 11 -methanol with methyl iodide, can be detected by only radiolabeling, hereby the origin of the newly synthesized methyl iodide is manifested.