Maria Giorgia Cutrufello

4-Methylpentan-2-ol dehydration over zirconia catalysts prepared by sol-gel

Zirconia samples have been prepared from xerogels and aerogels obtained using zirconium n-propoxide as precursor. Structure and texture have been investigated by X-ray diffraction, thermal analysis, transmission electron microscopy, nitrogen adsorption/desorption. Surface acidity and basicity have been assessed by adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. 4-Methylpentan-2-ol dehydration has been tested at atmospheric pressure in a fixed-bed flow microreactor. The xerogel gives tetragonal zirconia upon calcination, during which a mesoporous system is formed. The crystal phase depends on the presence of oxygen during the cooling step in the case of the aerogel, whose texture is partially retained upon calcination. Both kinds of catalysts have well-balanced concentrations of acid and base sites, but the acid sites are weaker in comparison with the basic ones. At 603 K the initial conversion of 4-methylpentan-2-ol over the calcined xerogel and aerogel is 45 and 63%, respectively; the selectivity to 4-methylpent-1-ene is 77% for both. The occurrence of an E2-like mechanism with the activated complex having a marked carbanionic character seems probable. The aerogel catalyst is quite stable during operation, whereas changes in activity and selectivity are observed for the xerogel catalyst.

MeOx/SBA-15 (Me = Zn, Fe): highly efficient nanosorbents for mid-temperature H2S removal

Zinc oxide/ and iron oxide/SBA-15 composites were synthesized using the innovative Two-Solvents procedure and tested as sorbents for the mid-temperature (300 °C) removal of hydrogen sulphide, and then compared with a commercial unsupported ZnO sorbent. The sulphur retention capacity results showed the superior performance of the iron oxide/SBA-15 composite (401 mg S g−1 Fe2O3) in comparison with the zinc oxide/SBA-15 composite (53 mg S g−1 ZnO), both these sorbents being much more efficient than the commercial sorbent (6 mg S g−1 ZnO). The different sorption behaviour was discussed in terms of the nature of the nanocomposites where: (i) the mesostructure of the support was retained with a high surface area and pore volume; (ii) the zinc oxide phase was incorporated inside the SBA-15 channels as a thin amorphous homogeneous layer while the iron oxide was dispersed in form of small maghemite crystallites; and (iii) significant interactions occurred between the silica matrix and the zinc oxide phase. Remarkable differences in the regeneration behaviour of the exhaust sorbents were revealed by temperature-programmed experiments under an oxidizing atmosphere. After regeneration, the sorption properties of the zinc oxide/SBA-15 composite appeared to be enhanced compared to the commercial sorbent. Incomplete recovery of the sorption activity was observed for the regenerated iron oxide/SBA-15 sorbent, whose performance remained far better than that of the ZnO-based one, either fresh or regenerated. In view of its higher sulphur retention capacity and appropriate regeneration temperature (T ≤ 350 °C), the iron oxide/SBA-15 composite is a promising material for the design of advanced sorbents for a thermally efficient H2S removal process from hot gas streams.

CeO2–La2O3 catalytic system. Part II. Acid–base properties and catalytic activity for 4-methylpentan-2-ol dehydration

CeO2–La2O3 mixed oxides, formerly prepared ia a sol–gel procedure and characterised by several techniques, have been further investigated as to their acid–base properties and catalytic activity. Surface acidity and basicity have been assessed by adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. Catalytic activity for 4-methylpentan-2-ol dehydration has been tested at atmospheric pressure in a fixed-bed flow microreactor. The acid and base features of the catalysts markedly depend on the relative amounts of the two component oxides. For pure ceria, cerium and oxygen ions are the source for acidity and basicity, respectively. Some contribution of OH groups to the acid–base character is probable for the mixed oxides. Most of the acid sites of each catalyst are weak, whereas most of its base sites are strong. The concentration of the base sites tends to prevail over that of the acid sites as the lanthanum content increases. 4-Methylpent-1-ene is by far the most abundant product of 4-methylpentan-2-ol conversion for all the catalysts, which are quite stable, even after repeated operation cycles. Subtle differences in the relative extents of dehydration and dehydrogenation activity seem to be due to a shift in the reaction mechanism, originated by changes in the relative amounts of acid and base sites.

Catalytic activity of a ceria-lanthana system for 4-methylpentan-2-ol dehydration

A ceria-lanthana catalytic system prepared by the sol-gel technique proved to be active in 4-methylpentan-2-ol conversion, mainly leading to 4-methylpent-1-ene, a monomer for manufacturing polymers of high technological properties. The product distribution strongly depends on the acid-base features of the catalyst. The catalytic behavior of the samples was examined in the light of their acid-base properties.

ACID-base properties of a CERIA-lanthana catalytic system

A ceria-lanthana system was prepared by the sol-gel technique in order to obtain active catalysts for the 4-methylpentan-2-ol conversion. As the products distribution strongly depends on the acid-base features of the catalyst, acidity and basicity of the CeO2-La2O3 samples were determined by adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. Both concentration and strength of the sites were assessed and their nature was investigated by analysing the microcalorimetric data in the light of the structural and textural characterisation previously carried out. Present samples are compared to a formerly investigated ceria-lanthana system prepared by a different procedure.

Remarkable acid strength of ammonium ions in zeolites: FTIR study of low-temperature CO adsorption on NH4FER

FTIR spectra of CO adsorbed at 100 K reveal remarkable acid strength of the free NH groups of tridentate ammonium ions in NH4FER zeolite.

Conversion of 4-methylpentan-2-ol over powder catalysts prepared by ball milling

Amorphous powders prepared by mechanical alloying were tested as heterogeneous catalysts in the 4-methylpentan-2-ol conversion into its dehydration and dehydrogenation products. The reaction was performed both in a conventional fixed-bed flow microreactor and in a modified milling vial used as a mechanochemical batch reactor. In the thermal catalytic tests several amorphous alloys, CuM (M = Ti, Zr, Hf), PdZr, and CuPdZr were employed as catalysts. Pretreatment conditions and catalytic runs induced different structural evolution in the tested systems. A correspondence was observed between structural modifications and catalytic properties. The mechanochemical trials were performed over a-Cu40Hf60 powders. Conversion and selectivity results were found to depend on the impact energy. The determination of the milling dynamics parameters allowed evaluation of the mechanochemical activity and comparison of, on an absolute basis, the results of the catalytic trials performed by the two techniques.

Hydroxylation of benzene to phenol with nitrous oxide on Fe-silicalites

The title reaction was studied, at 623 K and atmospheric pressure, over Fe-silicalites with different Fe 2 O 3 content. The best results were obtained for the sample with a Fe 2 O 3 content of 0.82 wt %. FTIR spectroscopy was used to investigate the nature of the extrafrarnework iron species in Fe-silicalites using NO as probe molecule.