NaY Catalyst Research Articles

Synthesis of organic sulfides using Ce-exchanged NaY catalyst

Synthesis of organic sulfides from thiols and alkyl halides is achieved using Ce-exchanged zeolite catalyst, Ce(72%)NaY.

Molecular catalyst design. Synthesis, characterization and properties of zeolite NaY catalysts made with a tetranuclear copper(II) complex

Highly active oxidation catalysts have been made by treating dehydrated zeolite NaY with excesses of the neutral tetranuclear copper(II) precursor ( μ 4-O)L 4Cu 4Cl 6 (A, L = N,N-diethylnicotinamide) in methylene chloride, followed by methylene chloride washing, drying and oxidation with O 2 at 220°C. The loaded samples contain from 3.4 to 14.3% w/w total copper, depending on the amount of A used. Previous measurements with a different ‘titration’ loading method together with analytical and spectroscopic data for materials loaded with different excesses of A indicate 2.9–13.8% w/w copper on the zeolite surface (50 m 2/g) due to a zeolite-solution equilibrium with A. Oxidation of the most heavily loaded sample with O 2 gives a catalyst that is ten times more active per gram for CO oxidation than bulk CuO at 450°C. The most lightly loaded sample oxidizes CO 115 times faster than bulk CuO on a per gram CuO basis. Turnover numbers at infinitely dilute CuO loading approach 75% of the TON for bulk CuO, suggesting that CO oxidation on bulk CuO involves more than one CuO site. Prospects for catalyst development through transmetallation chemistry and different loading methods are discussed.

Interconversion of unsaturated C 4 nitriles under basic conditions II. Catalytic and FTIR study over basic zeolites

A study was made of the interconversion of isomeric unsaturated C 4 nitriles (allyl cyanide, crotononitrile and methacrylonitrile) over strongly basic Na NaY , and for comparison on neutral NaY and acidic CaY catalysts at 623 K. Pulse experiments indicated the facile transformation of allyl cyanide to crotononitrile and the low reactivities of crotononitrile and methacrylonitrile. FTIR studies of the adsorbed molecules revealed the possible involvement of anionic intermediates.

Highly Selective Catalytic Reduction of NO by H2over Au0and Au(I) Impregnated in NaY Zeolite Catalysts

The NO–H2reaction has been studied over Au0/NaY and Au(I)/NaY catalysts, which were prepared by the mechanical mixing of AuCl3with NaY zeolite and by the monolayer dispersion of Au(I) species into NaY zeolite, respectively. The precursor samples were reduced in flowing hydrogen at 423 K. The NO–H2reaction over these catalysts took place at relatively low temperatures under isothermal conditions from 373 to 673 K. The Au(I)/NaY catalysts were more active toward the above reaction compared with the Au0/NaY catalysts. The NO selectivity was pointed to the N2and N2O formation, with the former catalysts being more selective to N2.In situFT–IR study of the NO–H2reaction on the gold catalysts demonstrated that NH3was detected in the adsorbed NH4+form at 1440 cm−1, along with N2O at 2240 (2220) cm−1and H2O at 1645 cm−1. Two characteristic bands due to the vibrations of N–O bond in adsorbed NO were identified. The bands at 1880 cm−1in the spectra of Au0/NaY were assigned to Aun+–NO (n≈0) complexes, and the corresponding bands at 1910 cm−1in the spectra of Au(I)/NaY were assigned to Aun+NO (n=1) complexes in cages of zeolite. It was proposed that N2O and NH3formed simultaneously at low to moderate temperatures (<500 K) by the addition of N atom to NO and H atoms, respectively. The presence of adsorbed N atoms was confirmed by the coadsorption of NO/CO/H2mixture onto Au(I)/NaY at 423 K, where a band at 2280 cm−1ascribed to isocyanate [NCO] intermediate was developed intensively with time. This band did not deliver when a mixture of NO/CO was admitted alone to the IR cell. Therefore, the H atom promoted the N–O bond fission to form Nadand OHad. The [NCO] species is the result of a reaction between the adsorbed N atom and gaseous CO.

Molecular metal carbonyl clusters and volatile organometallic compounds for tailored mono and bimetallic heterogeneous catalysts

Specific studies carried in Milan laboratory in the application of metal carbonyl clusters to preparation of supported catalysts are reviewed. Examples are reported of catalysis by heterogeneous organometallic surface species, such as 1-butene isomerisation catalysed by silica-anchored osmium carbonyl species, or of catalysis by very small metal particles produced under catalytic conditions, such as ethylene hydroformylation using silica supported [Rh 12(CO) 30] 2− as precursor. Highly active bimetallic FeIr MgO catalysts for methanol synthesis, have been pr prepared by controlled reductive decomposition of physisorbed [Et 4N] 2[Fe 2Ir 4(CO) 16] and [Et 4N] 2[Fe 2Ir 2(CO) 12] clusters. In these examples, evidence of the nature of the catalytic entities is reached by in situ DRIFTS characterisation under catalytic conditions or using EXAFS measurements. Metal particles deposited inside the zeolitic cavities have been obtained by mild reduction conditions of entrapped organometallic compounds introduced by chemical vapour deposition (CVD). In this way, non-acidic Pt KL , Pd NaY catalysts for hydrocarbon reforming have been prepared. Bimetallic Pt Re and Rh Mn particles, entrapped inside a NaY zeolite, have been easily obtained by CVD of M 2(CO) 10 carbonyls (M  Re, Mn) on pre-reduced metal particles.

Hydrodesulfurization of Dibenzothiophene on Iron-Exchanged Y Zeolite

Abstract An Fe(II)HY zeolite catalyst pretreated at 500 and 600 °C was highly active for the hydrodesulfurization of dibenzothiophene when the Fe(II)HY zeolite was exchanged in a solution of FeCl2 and aqueous NH3 with NaY in N2 gas, whereas the Fe(III)NaY catalyst in a solution of FeCl3 displayed a low activity.

Stability and catalytic properties of Mo-containing Y-type zeolite catalysts calcined by an isobaric thermal decomposition procedure

A study has been made of the effect of calcination temperature, under isobaric thermal conditions, on the structural stability and catalytic activity for thiophene conversion of Mo-impregnated NaY and NH 4NaY zeolite catalysts. The IR spectra, X-ray diffraction, BET surface area and sorption capacity results indicated that catalyst crystallinity was largely preserved after treatment at 110°C, and decreased substantially after calcination at over 350°C. All Mo-containing zeolite catalysts remained stable in air.

Ethanol oxidation over Y-type zeolite ion-exchanged with copper(II) and cobalt(II) ions

A study was made of the gas-phase oxidation of ethanol over Cu(II) and Co(II) ion-exchanged Y-type zeolite catalysts (Cu(II)NaY and Co(II)NaY) in the temperature range 523 to 623 K in a flow system. As the oxidation product, the partial oxidation product, acetaldehyde, was formed almost selectively over both Cu(II)NaY and Co(II)NaY catalysts. From the dependence of the oxidation activity on the percentage of replaced Cu(II) or Co(II) ions, the active sites for oxidative dehydrogenation of ethanol were found to be the Cu(II) or Co(II) ions ion-exchanged by Na + ions in Y-type zeolite. From the kinetic studies of acetaldehyde formation over both the Cu(II)NaY and Co(II)NaY catalysts by means of a differential flow reactor, the formation rate of acetaldehyde was reciprocal first order in ethanol and one-half order with respect to the partial pressure of oxygen, irrespective of the Cu(II) or Co(II) ion-exchanged Y zeolite catalyst ( r CH 3CHO = kP −1 C 2H 5OH P 1 2 O 2 ). The activation energies for the formation reaction of acetaldehyde over the Cu(II)NaY and Co(II)NaY catalysts were 70.0 and 64.7 kJ/mol, respectively, in the range 523 to 623 K. A mechanism for the formation of acetaldehyde over Cu(II)NaY and Co(II)NaY is proposed and satisfactorily agrees with the kinetic results experimentally obtained, in which the rate-determining step seems to be the surface reaction between the adsorbed ethanol and the dissociatively adsorbed oxygen.

Carbon monoxide chemisorption on a Pt–NaY catalyst. Part 1.—Determination of the distribution of the chemisorbed carbon monoxide phase by a 129Xe-nuclear magnetic resonance study of adsorbed xenon

By using 129Xe as an n.m.r.-detectable probe it has been possible to determine quantitatively the distribution of CO molecules chemisorbed on small platinum particles (containing on average six atoms) located in the supercages of NaY zeolite. At 25 °C CO molecules are chemisorbed on the first particles encountered on entering the zeolite crystallite, with a coverage of one CO molecule per two Pt atoms. In contrast, at 300 °C one can obtain, at low coverage, a homogeneous distribution corresponding to only one CO molecule per particle.

Carbon monoxide chemisorption on a Pt–NaY catalyst. Part 2.—Influence of carbon monoxide coverage and of coadsorbed molecules on the infrared spectrum of adsorbed carbon monoxide (electron transfer and dipole–dipole coupling)

By means of the results obtained by 129Xe n.m.r. spectroscopy for the local distribution of CO chemisorbed on the very small platinum particles (six atoms on average) supported on NaY zeolite, it has been possible to determine precisely the effects of back-donation from the metal to CO and of dipole–dipole coupling between chemisorbed CO on the variation of vCO with surface coverage. The effect of dipolar coupling predominates when the coverage rises from one CO molecule per particle to saturation, but back-donation increases at the same time. The latter could be due to the small size of the particle and/or to the acidic nature of the support.

Oxidation of benzyl alcohol over Co(II)NaY zeolites

Benzyl alcohol oxidation was carried out with a Y-type zeolite catalyst ion-exchanged with cobalt(II) ion (Co(II)NaY) in a flow system operated at atmospheric pressure and temperatures of 320 to 390 °C. The Co(II)NaY catalyst was found to have high selectivity for benzaldehyde, a partial oxidation product, in comparison with that of Cu(II)NaY catalyst. The catalytic activity was proportional to the degree of Co(II) ion exchange up to a level of about 65 to 70%. This dependence of the oxidation activity of Co(II)NaY catalyst upon cobalt(II) ion content emphasizes the importance of this exchanged cobalt(II) ion as the main active site for benzyl alcohol oxidation. The rate of formation of benzaldehyde was second order in benzyl alcohol and 0.5 order in oxygen ( r φCHO = k · [ φCH 2OH ] 2 · [ O 2 ] 1 2 ). An activation energy of 25.6 kcal/mole was observed in the temperature range 320 to 390 °C. The effect of amine addition in the Co(II)NaY catalytic system was investigated by the variation of the amount of amine addition. The addition of pyridine or piperidine increased the oxidation activity, while the addition of ethylenediamine decreased the oxidation activity. Increased concentrations of ethylenediamine resulted in the complete deactivation of Co(II)NaY catalyst for this oxidation. Cobalt(II)-pyridine or -piperidine adduct formation within the large cavities of a Co(II)NaY catalyst was demonstrated by infrared measurements. A mechanism for benzaldehyde formation over Co(II)NaY catalyst, in which dissociative oxygen species participate as a form of [CoO], is proposed on the basis of the kinetic result obtained here. The presence of the dissociative oxygen species adsorbed on cobalt ions was suggested to contribute to the high selectivity for benzaldehyde, a partial oxidation product of benzyl alcohol.

Chromatographic study of the adsorption of hydrogen on zeolites

1. The processes involved in the adsorption of hydrogen on NaY, HY, and NaM catalysts vary with the temperature. Over the interval from 20 to∿ 300°C, the values of the heat (Q) and entropy (AS) of adsorption are 1.4–1.8 kcal/mole and −8 to −9 e.u., respectively. Over the interval from 300 to 500°C the heat of adsorption is equal to zero and ΔS=−5 to −6 e.u. 2. The value of the entropy of adsorption of hydrogen at low temperatures is close to the value calculated theoretically for nonlocalized molecular adsorption and localized dissociative adsorption. At higher temperatures, the entropy of adsorbed hydrogen is close to the value calculated for nonlocalized dissociative adsorption.

Isomerization of &lt;i&gt;n&lt;/i&gt;-Pentane over Sodium Y Zeolite Exchanged by Palladium and Platinum

Isomerization of n-pentane was investigated mainly by pulse technique in the temperature range from 300°C to 420°C using zeolite Y catalysts in which park of the Na+ ions were exchanged by ammine complex ions of palladium or platinum. These catalysts were found to be more selective than palladium or platinum supported on silica gel for n-pentane isomerization to isopentane against hydrogenolysis. Particularly, on Pd/NaY catalysts no hydrogenolysis could be observed, and isomerization took place exclusively.Isomerization selectivity of NaY catalysts containing Pd or Pt was, however, strongly influenced by pretreatment in a stream of air prior to reduction. Palladium or platinum in the zeolite catalysts which were pretreated in air at temperatures near 300°C and reduced at 450°C was so highly dispersed that X-ray measurement could not detect crystals of these metals. Such treatment enhanced hydrogenolysis activity and reduced isomerization selectivity. On the other hand, selective catalysts for isomerization of n-pentane were obtained by reduction of those NaY catalysts containing Pd or Pt which were pretreated at below 250°C or above 350°C. Reduction of the catalysts pretreated under these conditions formed relatively large sized crystals of Pd or Pt on the outer surface of the zeolite particles.From the results, it was implied that isomerization over NaY catalyst containing Pd or Pt would be promoted by protonic acid sites which were formed in the reduction processes of transition metal-ammine complex ions to metals.

Transformations of isobutylene in the presence of synthetic zeolites

1. Isobutylene is converted to a mixture of C3 and higher olefins with the predominance of octenes in a flow system at atmospheric pressure and 150–350° on NaA, CaY, and NdX zeolites. 2. The greatest catalytic activity was manifested by NaY and NdX catalysts, while the greatest selectivity in the dimerization of isobutylene was displayed by NaA and NaY. The yield of octenes in the presence of the latter reaches 94–96%.