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A series of bifunctional bimetallic PtCu/H[Al]ZSM5-type catalysts was prepared and acetone transformation was carried out over them at 160 °C, 1 atm, acetone/hydrogen molar ratio=3, and WHSV (weight of reactant injected per weight of catalyst per hour) ranging between 9.4 and 38 h$^-1$. According to the results, as copper atomic fraction (X(Cu)) increases in the bimetallic catalyst, propane formation rate decreases and methyl isobutyl ketone (MIBK) formation rate increases until X(Cu) equals 0.40. These results suggest that active metallic centers for the olefin double bond hydrogenation in the α-β unsaturated ketone, which leads to the MIBK formation, do not appear to be those hydrogenating the acetone carbonyl double bond to form propane. When X(Cu)>0.40, MIBK formation rate considerably decreases, meaning that practically all platinum metallic centers have been passivated for those copper atomic fractions over the PtCu/H[Al]ZSM5-type catalyst. Therefore, catalysts begin to act only by means of the acid function, and as a result a logical increase in the mesityl oxide (MO) concentration occurs, a substance that is formed by means of an acid catalysis.

Acetone transformation into methyl isobutyl ketone (MIBK) was studied using a fixed-bed dynamic reactor at 160°C, 1 atm pressure and acetone/H2molar ratio=3. The reaction was carried out over Pt/HMFI bifunctional catalysts, with 0.30 wt% of platinum which was supported over three aluminosilicates (Si/Al ratio=40, 95 and 160) and a borosilicate (Si/B ratio=44) with similar dispersion. The results show that catalytic properties depend greatly on density and strength of the acidic sites of the catalysts. Moreover, the limiting step of the MIBK synthesis reaction (aldolization of two acetone molecules) is carried out over the acidic sites of the aluminosilicates, but not over those of the borosilicate, which considerably affects reaction selectivity.

Methyl isobutyl ketone (MIBK) was synthesized from acetone (Ac) and hydrogen over Pt-HZSM5 bifunctional catalysts. The reaction was carried out at 160°C, atmospheric pressure, and with a PH2/PAc molar ratio = 0.33, using a fixed bed and dynamic flow reactor. The results show that catalytic properties and coke formation largely depend on the ratio between the number of accessible hydro-dehydrogenation sites and the number of theoretical acidic sites (nPt/nA).

The aromatization of propane at 530°C on three MFI gallosilicates (Si/Ga = 30, 50 and 180) and on a MFI aluminosilicate (Si/Al = 30) was investigated. After pretreatment at 530°C under dry air flow, 30 Al MFI was seven times more active than 30 Ga MN. This can be related to the greater strength of the acid sites of the aluminosilicate sample, which was shown by a calorimetric study of ammonia adsorption and by ammonia thermodesorption. On all the catalysts propene and methane + ethene in quasi-equimolar amounts appeared as primary products, whereas ethane, butenes, butanes, C+₅ olefinic and naphthenic compounds, and C₆-C₈ aromatics were secondary products. However, large differences were found in the product distribution, namely a lower initial cracking/ dehydrogenation ratio on 30 Ga MFI, greater selectivity to aromatics, and lower selectivity to alkanes (C₁, C₂, C₄) at high conversion, which can be explained by a dehydrogenating effect of gallium. The product distribution depended also on the Si/Ga ratio of the gallosilicate, a better selectivity to aromatics being found with 30 Ga MFI. The selectivity differences are mainly due to differences in the acid site density. The treatment of gallosilicates at 700-800°C under dry air flow caused a significant increase in their activity and in their selectivity for propane aromatization. This could be related to the formation of a small amount of extraframework gallium species, well dispersed in the crystallites and highly active for dehydrogenation of propane and of naphthene intermediates. On these catalysts propane aromatization occurred mainly through a bifunctional scheme and the formation of unwanted C₁-C₂ products, through acid cracking was very limited. The effect of the pretreatment temperature on the acid and dehydrogenating activity of the 30 Ga MFI sample showed that framework gallium species were much less active for dehydrogenation than extraframework species and indeed are probably inactive.Copyright 1994, 1999 Academic Press

The dealumination of a NH4NaY zeolite through hydrothermal treatment at 500 ° C and 650 ° C occurs apparently through a kinetic law of the second order with respect to aluminium. The kinetic order is actually equal to one when the hydrolyzable aluminium atoms only are taken into account i.e. those to which ammonium ions and not sodium ions are associated.

Propane aromatization (530°C, 1 atm) was used as a reaction model to evaluate the effect of the calcination temperature on the catalytic properties of an as-synthesized [Ga1.3]-ZSM-5 zeolite obtained from alkali-free media and calcined at two different temperatures: 530°C (C-530) and 750°C (C-750). Results show that in spite of its lower acidity, C-750 is more active and selective toward aromatics than C-530. This is probably due to the fact that at higher temperature the decomposition of organic compounds used during the zeolite synthesis is accompanied by a partial degalliation of the zeolitic support leading to the production of a bifunctional x“Ga2O3” /H-[Gay-ZSM-5(2x+y=1.3)catalyst.

The steaming of as-synthesized alkali-free TPA-MeNH3-[Ga0.99Al1.99]-ZSM-5 zeolite was carried out at temperatures of 530°C (St-530), 550°C (St-550), and 600°C (St-600). Physical characterization of the solids was carried out by XRD, IR, N2 adsorption, and27Al and71Ga MAS-NMR. n-Heptane cracking (T=350°C; PN2/PnC7=4; P=1 atm) was used as a model reaction to characterize the acidity of the catalysts. Propane aromatization (T=530°C; P=1 atm) was used to characterize the acid or the bifunctional behavior of solids. Results show that steaming produces less acid solids due to degalliation and dealumination of the zeolite structure. Because the presence of steam reduces the temperature at which the formation of extra framework gallium species occurs, bifunctional “Ga2O3”/H-[Ga,Al]-ZSM-5 catalysts are formed at lower temperature (T=530°C) in comparison when calcination is carried out under dry air. Catalysts are less selective to BTX as steaming temperature increases because of a strong reduction of Bronsted acid sites.

Synthesis of 4-methyl-2-pentanone, better known as methyl isobutyl ketone (MIBK), from propanone (Ac) was studied in a fixed-bed and a flow reactor at 160 °C, 1 atm and an H2/Ac molar ratio equal to 0.33, using Pt-H[Al]ZSM5 bifunctional catalysts with variable platinum percentage and Si/Al ratio. The results show that initial total activity to all measured products at t = 0, per acidic site (Ao/nA), residual activity (Ar= A265/A0, ratio of activity after 265 min of stream and the initial total activity to all measured products at t = 0) and initial formation rate of each product per acidic site (Ro/nA) largely depend on the relationship between the number of hydro-dehydrogenating metallic sites and the number of theoretical acidic sites (nPt/nA) present in the catalysts used.

The introduction of platinum in a protonic offretite causes a decrease of its activity for m-xylene isomerization and an increase of its constraint index. This is due to the blockage of the offretite channels by small platinum crystallites (<8 Å), as confirmed by the study of m-xylene adsorption.

Sodium exchange and ammonia selective poisoning of the acid sites of an HY zeolite (Si/Al=20) were carried out and their effects on the catalytic properties for the alkylation of phenol with methanol (200‡C, 1 atm and N2/reactants molar ratio of 4) were evaluated. Results show that the reaction is highly sensitive to the number and strength of the acid sites of the catalyst. A decrease in the number of acid sites by sodium exchange of the protons or by ammonia selective poisoning produces important changes in the selectivity of the reaction. In fact, a high increase in the anisole/cresol ratio is observed as the percentage of exchanged sodium in the zeolite increases, while the ammonia selective poisoning shows that at low desorption temperatures (?250‡C) only anisole is formed while at higher desorption temperatures both anisole and cresols were observed. These results show that anisole formation requires sites with lower acid strength compared to those necessary for cresol formation.