Hanna Marczewska

Acidity of sulfated oxides: Al2O3, TiO2 and SiO2. Application of test reactions

The acidic properties of different oxide/SO42− type superacids have been studied. Test reactions indicated that the acid strength of the Al2O3/SO42− system changed considerably with H2SO4 surface content notably −7.05 < H0 < −10 (1%), −10 < H0 < −14 (2–3%), H0 < −14 (4–9%), while for TiO2/SO42− preparations it was high and less dependent on catalyst composition: H0 < −14 (≥1%) and finally for SiO2/SO42− catalysts it was low with −0.75 < H0 < −3.50 (1–9%). Alkane isomerization over Al2O3/SO42− and TiO2/SO42− catalysts was observed to begin with the formation of an unsaturated intermediate state through the action of redox centres. Further alkene transformation into carbenium ion in the presence of Bronsted sites (Al2O3/SO42−) or secondary Bronsted centres (TiO2/SO42−) allows skeletal alkane isomerization to proceed.

Oxide catalysts for methane transformations in the absence of oxygen

The possibility of methane transformation to higher hydrocarbons in non-oxidizing atmosphere has been studied. It was found that in the presence of the MnOx−Na/SiO2-HZSM-5 catalytic system methane can be transformed into aromatics with a yield similar to that reported for oxidative coupling conditions.

Catalysts for methane transformations into aromatics

The possibility of methane to aromatics transformation in non-oxidizing atmosphere has been studied. It was found that in the presence of the MnOx−Na/SiO2-HZSM-5 and CuO−FeO/HZSM-5 catalyst systems methane can be converted into aromatics with a yield depending on zeolite acidity.

Catalysts for methane transformation in the absence of oxygen, II. Nature of active centers

The activity of supported manganese oxide catalysts doped with copper, chromium and iron oxides in methane to higher hydrocarbons transformation in non-oxidizing atmosphere has been studied. Chromium and iron oxides are more effective promoters than copper oxide. Redox centers of dehydrogenation ability are active in methane transformations.

Acidity of the silica–alumina/BX3 superacids

Acid properties of the catalysts obtained by the reaction of boron halides solutions with silica–alumina containing 87% of SiO2 were studied. It was found that the strength of the acid sites formed depends on boron halide used and the nature of BX3 solvent. The stronger acceptor properties of BX3 the higher acid strength of SiO2(87%)-Al2O3/BX3 catalysts was observed. For the preparations obtained by the action of BX3 1.0 M solutions in CH2Cl2 the following order of superacid properties, conformable with halides acceptor strength, was found: SiO2–Al2O3/BI3 > SiO2–Al2O3/BBr3 ≫ SiO2–Al2O3/BCl3 ∼ 0. The BX3 solvent basicity influences the acid strength of acid centres formed. The less basic is the solvent used, the higher is the strength of the acid sites formed. The experiments with selective poison of Bronsted acid centres (2,6-di-tert-butylpyridine) proved that superacid and strong acid sites of SiO2(87%)–Al2O3/BX3 catalysts are of protic nature.

BCl3/silica–alumina superacid

The solid superacid of BCl3/silica–alumina type was studied. It was found that a suitable carrier for superacid synthesis with BCl3 vapours should possess OH groups with strong acid properties situated in the proximity of strong Lewis centres. Superacid Bronsted centres are formed as a result of the reaction between adjacent OH groups (at least one of which should be of high acid strength) of the carrier and BCl3.