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.

The transformation of cyclohexanone was carried out on a series of bifunctional PdHFAU catalysts with Pd contents between 0.1 and 0.5wt.% and framework Si/Al ratios equal to 5, 20, 40 and 100, under the following conditions: flow reactor, 473K, pressures of cyclohexanone and hydrogen equal to 0.17 and 0.83bar, respectively. With all the catalysts, cyclohexylcyclohexanone, the formation of which requires successive steps of aldolization, dehydration and hydrogenation, is directly formed. The effect of the balance between the hydrogenating and acid functions of the catalysts (taken as the ratio between their activity for toluene hydrogenation and their number of protonic acid sites, AH/B) on their activity, stability and selectivity is the one expected from a bifunctional catalytic process. The activity per protonic site first increases with AH/B, then remains constant above a certain value of AH/B (0.4h−1), the limiting step of cyclohexylcyclohexanone formation being then cyclohexanone aldolization. The selectivity to cyclohexylcyclohexanone as well as the stability increase with AH/B remaining constant for AH/B>1h−1. While a high selectivity to cyclohexylcyclohexanone is obtained, the catalyst stability is relatively poor due to the retention inside the zeolite micropores of polar tricyclic C18 compounds.

The gas phase transformation of acetone, cyclohexanone and acetophenone was investigated in a fixed bed reactor over series of bifunctional Pt and Pd/molecular sieves (HFAU, HBEA, HMFI, HMCM41). Ketones resulting from three successive steps: aldolisation and dehydration of the resulting ketoalcohols on the acid sites then hydrogenation on the metallic sites can be obtained in one apparent step. Various other bifunctional transformations of the reactant, of the ketone product alone or of both can also be observed. However, the ketone products can be obtained with a high selectivity by an adequate choice of the pore structure and the adjustment of the acid and hydrogenating properties. Thus the pores of the molecular sieves should be large enough to allow an easy desorption of the ketone products and narrow enough to limit the formation of very bulky secondary compounds and of coke. Whereas for acetone transformation into methylisobutylketone an average pore size zeolite (e.g. MFI) should be used, a large pore zeolite (e.g. FAU) is preferred for cyclohexanone transformation into cyclohexylcyclohexanone and a mesoporous MCM41 silicoaluminate for acetophenone transformation into 1,3-diphenyl-butan 1-one.

Acetone transformation into methyl isobutyl ketone (MIBK) was studied using a fixed-bed dynamic reactor at 160°C, 1 atm pressure and acetone/H 2 molar 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.

The transformation of acetophenone was carried out over a 0.5 wt.% Pd HFAU catalyst (Si/Al=17) under the following conditions: flow reactor, 250°C, pressure of ketone and hydrogen equal to 0.8 and 0.2 bar, respectively. The reaction products were identified either by comparison in GC with reference compounds: benzene (B), ethylbenzene (EB), styrene (EB=), cumene (IPB), isopropylbenzene (IPB=) and benzoic acid (BA) or through GC/MS coupling: 1,3-diphenylbutane (DPB), 1,3-diphenylbutenes (DPB=), 1,3-diphenylbutan-1-one (DPBO), 1,3-diphenylbut-2-ene-1-one (DPBO=) and 2,4-diphenyl-3-methylpentenes (DPMP=). These products are formed through three main reaction paths. DPBO= results from successive aldolisation of acetophenone and dehydration of the resulting alcohol over the protonic sites of the zeolite, DPBO from the hydrogenation of 1,3-diphenylbuten-1-one over the Pd sites (path 1). The formation of EB= involves hydrogenation of acetophenone followed by dehydration of the produced alcohol; EB results from EB= hydrogenation (path 2). DPB= can result from EB= dimerization (path 2) or from hydrogenation of DPBO followed by dehydration of the resulting alcohol (path 2). These reactions are similar to those observed during acetone and cyclohexanone transformation over bifunctional catalysts. In these reactions no alcohol intermediate is observed, which shows that alcohol dehydration is much faster than aldolisation and hydrogenation steps. The third reaction path which leads mainly to IPB, IPB= and BA, plays a significant role in acetophenone transformation whereas this path was very slow in acetone and cyclohexanone transformations. BA and IPB= result from acid cracking of DPBO=, IPB from hydrogenation of IPB=. IPB= undergoes also dimerization into DPMP= and IPB undergoes dealkylation into B over the protonic sites of the HFAU zeolite.

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 transformation of cyclohexanone into cyclohexylcyclohexanone was carried out on various Pt or Pd zeolite catalysts with Si/Al (or Si/Ga) ratios around 40 under the following conditions : now reactor, 473 K, pressures of cyclohexanone and hydrogen equal to 0.25 and 0.75 bar. The effect of the percentages of platinum or of palladium (from 0.1 to 0.5 wt%) was shown with series of Pt and PdHFAU catalysts. The initial activity first increased with metal content then remained constant for metal contents greater than or equal to 0.2 wt%, which is typical of bifunctional catalyzed processes. The initial activity did not depend on the metal but the selectivity to cyclohexylcyclohexanone was much higher with the PdHFAU sample (75% against 47% with PtHFAU, at a cyclohexanone conversion of 30%). The catalytic properties of,various 0.2 wt% Pt or Pd zeolite catalysts with average or large pore size (HMFI alumino and gallosilicates, HBEA, HMOR and HFAU) were compared. The higher selectivity to cyclohexylcyclohexanone was found with all the Pd zeolites while the initial activities of 0.2 wt% PtHMFI and PtHMOR were greater than those of the corresponding Pd samples. The initial activities and the selectivities of 0.2 wt% Pd zeolites depended on the zeolite pore structure. The PdHFAU catalyst which has the largest pores was the more active and the more selective to cyclohexylcyclohexanone.

Amide hydrolysis is a key step in the widespread strategy of protection/deprotection of amino groups for synthetic purposes, usually carried out in homogeneous phase with mineral acids. It is shown here that under mild conditions (batch reactor, liquid phase, 75 degrees C) large pore zeolites (HY, HBeta, HMOR) can catalyse the hydrolysis of various aromatic amides. The best results are obtained over HY zeolite samples with Si/Al ratios of 16 and 30: eg complete and selective hydrolysis of 2-nitroacetanilide after 2-4 hours reaction for a zeolite/substrate ratio of 0.5 g/mmol. For similar values of the Si/Al ratio HBeta and rather all HMOR samples are much less active than HY samples, which is probably related to diffusion limitations.

The transformation of acetone was carried out over a 0.4 wt% PtHMFI catalyst (SiAl = 60) under the following conditions: flow reactor, 160°C, pressures of acetone and hydrogen equal to 0.75 and 0.25 bar, respectively. Methylisobutylketone, propane and traces of mesityloxide are observed as primary products while the other main products: 2-methylpentane and diisobutylketone result from secondary transformation of methylisobutylketone. The reactivity of the reaction products and of probable intermediates: diacetone alcohol, isopropanol and propene was compared to that of acetone, which allows us to establish the complete scheme of acetone transformation. Acetone is competitively transformed through bifunctional catalysis into methylisobutylketone and into propane. The limiting step of methylisobutylketone formation is acetone aldolisation over the acid sites of the catalyst while that of propane formation is acetone hydrogenation over platinum sites. Methylisobutylketone undergoes the same competitive bifunctional transformations leading to diisobutylketone (limiting step: acid coaldolisation of acetone and of methylisobutylketone) and to 2-methylpentane (limiting step: hydrogenation of methylisobutylketone).

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).

2-(2-Hydroxyethyl)-pyridine was dehydrated to 2-vinyl-pyridine in liquid phase over solid acid catalysts, with very high selectivity and fairly good reaction rate at relatively low reaction temperature (160 degrees C). The catalytic activity is well correlated with the presence on the catalyst surface of medium to weak Bronsted acid sites. The analysis of "coke" left behind onto the catalyst and the effect of partial poisoning of catalytic activity by CO2 indicate that the reaction takes place through two mechanisms, involving either a Bronsted acid site or a couple of acid-base sites.

The transformation ofn-decane was studied at 473 K, 101 kPa andpH2/pn-decane=9 on a series of PtHY catalysts containing from 0.02 to 1.5 wt% platinum and with Si/Al atomic ratios of 3, 9, or 35. The ratio between the number of accessible Pt atoms and the number of acid sites on which the heat of ammonia adsorption is greater than 100 kJ mol−1(nPt/nA) was chosen for characterizing the balance between the hydrogenating and the acid functions. The activities, stabilities, and selectivities of the catalysts are definitely governed by this balance. For low values ofnPt/nA(<0.03), the activity per acid site is low, the deactivation is rapid andn-decane leads directly to all the isomerization and cracking products. For high values (≥0.17) the activity per acid site is maximal, the deactivation is very slow andn-decane transforms successively into monobranched isomers, dibranched isomers, and tribranched isomers plus cracking products. In this latter case the catalyst can be considered as anidealbifunctional catalyst, namely a catalyst on which only one transformation of the alkene intermediates on the acid sites can occur during their diffusion from the platinum sites on which they are generated to those on which they are hydrogenated. Therefore the reaction scheme ofn-decane transformation matches the reaction scheme of olefinic intermediates. From the product distribution established on ideal catalysts the mechanism of the transformation of olefinic intermediates can be deduced. Branching isomerization occurs through protonated cyclopropane and cyclobutane intermediates. The cracking products result from the β-scission steps of tribranched decenes which involve two tertiary carbenium ion intermediates (mode A) and from the β-scission steps of dibranched decenes which involve one tertiary and one secondary carbenium ion intermediate (mode B). The participation of the β-scission of mono, di, and tribranched decenes through mode C (via two secondary carbenium ion intermediates) is negligible. The rate constants of the various steps involved inn-decane transformation are estimated. They can be classified in the following order: A cracking>Methyl shift>Branching>B cracking>>C cracking.

In this review we will try to give an integrated view of the relation between the structure and the catalytic behaviour of zeolitic materials, covering both the compositional and the structural aspects. Due to the amount of work that has been done in this wide area of zeolite catalysis this will, necessarily, be an incomplete although, hopefully, unbiased work.The paper will refer, not only to the relation that can be observed with natural and as-synthesised zeolites, but also to the wide range of techniques that are currently available for the 'tuning' of the catalytic properties of zeolitic materials. A special emphasis will be placed in all the aspects concerning shape selective catalysis, which is certainly the most striking form of a structure-activity relationship in heterogeneous catalysis.

The transformation of cyclohexanone was carried out on PtHZSM5 catalysts under the following conditions: flow reactor, 473 K, pressures of cyclohexanone and hydrogen equal to 0.25 and 0.75 bar respectively. Six families of products were identified by GC or GC-MS analysis: C6 cyclic hydrocarbons 1, C12 bicyclic hydrocarbons 2 (e.g., cyclohexylcyclohexene), cyclohexenylcyclohexanone 3, cyclohexylcyclohexanone 4, phenylcyclohexanone 5, tricyclic ketones 6 (e.g., biscyclohexenylcyclohexanone). A reaction scheme is proposed to explain the formation of these products. Compounds 1 would result from the following steps: hydrogenation of cyclohexanone (probably in the enol form) on Pt sites, dehydration of cyclohexanol on the acid sites, hydrogenation or dehydrogenation of cyclohexene on Pt sites. Compounds 2 are mainly formed through successive transformations of 4: hydrogenation, dehydration…; 3 results from aldolisation of cyclohexanone followed by dehydration of the resulting alcohol, 4 from hydrogenation of 3, 5 from dehydrogenation of 3. The compounds 6 result from aldolisation of 3 with cyclohexanone followed by dehydration, hydrogenation and dehydrogenation steps. The dehydration of alcohols is much more rapid than aldolisation and hydrogenation—dehydrogenation steps. On a 0.2 PtHZSM5 catalyst with a platinum dispersion greater than 70%, aldolisation is slower than hydrogenation—dehydrogenation steps. The deactivation of the catalyst affects more the acid sites than the metallic ones.

The potential of zeolites as catalysts for the Friedel-Crafts deisopropylation of dehydroabietic acid methyl ester 1 was determined. HY zeolites were found as active catalysts converting 1 into methyl trans-podocarpa-8,11,13-trien-15-oate, 3, through isopropyl transfer to toluene used asa solvent. There is no formation of the cis isomer, contrarily to what is found with aluminium chloride, but other products resulting from the elimination of the methylcarboxylate group and cracking can be observed at 100 degrees C. A better selectivity of deisopropylation can be obtained by reducing the zeolite acidity through sodium exchange or through dealumination or/and by operating at a lower temperature.

The stability and the ratio of the isomerization to cracking rates increase very much with platinum introduction and the isomer and cracking product distributions are significantly modified. This can be explained by the change from an acid to a bifunctional mechanism. However, platinum has practically no effect on the rate of 2-methylhexane transformation. This could be attributed to the fact that neither on USHY nor on PtUSHY is the formation of the carbenium ions with a 2-methylhexane skeleton the limiting step.

The activity, the stability and the selectivity of a series of bifunctional PtHY catalysts containing 0.02 to 1.5 wt% platinum and having Si/Al atomic ratios of 3 or 9 were compared for n-hexane and n-heptane transformations at 250°C, 1 atm, pH2/Palkane = 9. The balance between the two functions was characterized by nPt/nA (nPt: number of accessible platinum atoms, nA: number of strong acid sites). Qualitatively the change as a function of nPt/nA of the catalytic characteristics is the same with n-hexane and with n-heptane: for low values of nPt/nA the activity per acid site is low, the stability is weak and monobranched isomers M, dibranched isomers B and cracking products C are formed directly from the reactant while for very high values the activity is optimal, the stability perfect and M, B, C are formed through a step-by-step process ("ideal" hydroisomerization catalyst). Quantitatively big differences exist. In particular in order to be "ideal", a PtHY catalyst must have a much lower nPt/nA ratio for n-hexane isomerization. Moreover the reactivity of n-hexane is much lower than that of n-heptane. These results are interpreted in the light of the types of carbenium ions and of their rearrangement and scissions implied in n-hexane and n-heptane transformations.

The transformation of methylcyclohexane was studied at 250°C, 1 atm, pH 2 /pMCH = 9 on a series of PtUSHY catalysts containing 0.02 to 1.5 wt % Pt with a dispersion equal to or higher than 70%. The same products are formed on all the catalysts: isomers (dimethylcyclopentanes and ethylcyclopentane) C 3 -C 7 alkanes, toluene. While the initial activity in aromatization is proportional to the number of accessible platinum atoms (nPt), the activity in isomerization + cracking does not depend on nPt. This could be related to the fact that methylcyclohexane forms rapidly a tertiary carbenium ion on the acid sites of USHY. However the stability and the ratio of the isomerization to cracking rates increase with nPt as is the case in heptane transformation. The isomer distribution is also significantly modified : no formation of 1,3-dimethylcyclopentane on USHY, formation of all the isomers on PtUSHY and a favored formation of ethylcyclopentane, the only isomer which can result from a type A rearrangement. On all the PtUSHY catalysts the formation of light products follows the isomerization. The amount of C 7 alkanes (ring opening products) is negligible in comparison to the amount of C 3 -C 5 products, the formation of which requires two scission steps. Mechanisms are proposed to explain the product distribution as well as the differences between methylcyclohexane and heptane transformations.

Abstract The platinum dispersion and the activity for benzene hydrogenation of Pt USHY and PtH mordenite catalysts prepared by exchange with [Pt(NH3)4]2+ were measured for various activation conditions. In both cases, highly Dispersed platinum was obtained for a calcination temperature under strong dry air flow of 300°C. Subsequent hydrogen treatment has practically no effect, Pt° being formed during calcination by autoreduction of the platinum complex. The turnover number of platinum for benzene hydrogenation is much lower on PtH mordenite than on PtUSHY catalyst. This can be explained by a blockage of the channels of this quasi monodimensional zeolite by the deposit in the first minutes of reaction of carbonaceous compounds formed by oligomerization of the benzene hydrogenation products.

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.