Pd-zeolite Catalyst Research Articles

Investigation of the Suzuki–Miyaura cross-coupling reaction on a palladium H-beta zeolite with DFT calculations

Metal or metal cluster-doped zeolites catalyse a wide variety of reactions. In this work, a coupling reaction between bromobenzene and phenylboronic acid to yield biphenyl with the Pd–H-Beta zeolite catalyst was investigated with density functional theory (DFT) calculations. Utilizing a model system with tetrahedral Pd4 clusters within the H-Beta zeolite, it was demonstrated that the catalyst exhibited notable reactivity by effectively reducing the activation energy barrier for the reaction. Our investigation revealed that the zeolite framework facilitated electron transfer to the Pd cluster, thereby increasing the reaction activity. The coupling reaction was shown to be exothermic and comprise three main steps: oxidative addition of bromobenzene (C6H5Br), transmetallation with phenylboronic acid (C6H5B(OH)2), and reductive elimination of biphenyl (C12H10). Specifically, in the transmetallation step, which was the rate-determining step, the C–B bond breaking in phenylboronic acid (C6H5B(OH)2) and the phenylboronate anion (C6H5B(OH)3–) were compared under neutral and basic conditions, respectively. This comprehensive study clarifies the mechanism for the reaction with the modified Pd zeolite catalyst and highlights the essential role of the zeolite framework.

Effect of Pd- precursor and support acid properties on the Pd electronic state and the hydrodesulfurization activity of Pd-zeolite catalysts

We studied on the function of Pd species located in mesopores and inside zeolite channels (micropores) of the montmorillonite-modified zeolite catalyst for the hydrodesulfurization of diesel fraction with 350 ppm of sulfur as DBT, 4-MDBT, and 4,6-DMDBT. It was shown that the ex-dihydrogentetrachloropalladate impregnated catalyst as well as the ex-tetraamminepalladium(II) chloride ion-exchanged catalyst have high efficiency of sulfur removal from the diesel fuel in temperature range 280–300 оC.The sulfur tolerance of catalyst depended on the method of Pd adding. The catalyst prepared by ion-exchange with tetraamminepalladium chloride solution exhibited the highest sulfur tolerance. According to FTIR of adsorbed CO, this catalyst contains a small Pd metal atoms or cluster in electron-deficient state inside zeolite channels. They probably ensure sulfur tolerance due to hydrogen spillover.The montmorillonite addivite significantly modifies performance of the Pd-Zeolite catalyst in hydrotreating of diesel fraction. It leads to a decrease of cracking function, while those of hydrogenolysis of sulfurorganic molecules and hydrogenation of aromatic molecules are strengthened in comparison with the unmodified catalyst. This effect is explained by the change of acidic properties of the catalyst, limitations of diffusion of various molecules into the zeolite channels, and diffusion of Pd from the zeolite channels.

Synthesis of pyrrolo-heterocycles via Pd-loaded zeolite catalyzed annulation of o- haloaromatic amine with terminal alkynes

A Pd-loaded zeolite-catalyzed heteroannulation of various 2-iodopyridines and 2-iodoquinolines with terminal alkyne is demonstrated. This approach provides a rapid and convergent synthesis toward a diverse range of pyrrolo-pyridines (azaindoles) and pyrrolo-quinoline ring systems. The Pd-zeolite catalyst can be reused within the same reaction without reactivation of the Pd-zeolite catalyst. Furthermore, Pd-zeolite catalysis is an interesting alternative to homogeneous catalysis for the synthesis of heterocycles.

Zeolite supported palladium nanoparticle characterization for fuel cell application

Palladium (Pd) has been widely used as a type of hydrogen storage material and has attracted much attention for fuel cell applications, due to its high solubility and mobility of hydrogen in Pd. In this study, Pd nanoparticles made by 1.5 wt% Pd loading on Y-zeolite under pre-treatment was employed to investigate their electrochemical activities using cyclic voltammetry (CV), and detailed local structural characterization of Pd cluster was probed by the extended X-ray absorption fine structure. Pd nanoparticle sizes were predicted at 0.81 nm–1.2 nm and the CV measurement has demonstrated that Pd zeolite catalyst has exhibited a similar tendency to those 40% Pd on XC-72R carbon. The hydrogen spillover process and surface conductance pathways contribute to the electrochemical behavior on Pd surface. In electrochemical environment, hydrogen is able to form hydride phase on Pd surface by either direct hydrogen adsorption or migrating to the centre of Pd.

Oscillations on CO Oxidation in a Pd Zeolite Catalyst: Effect of Diffusion and Poisoning of Reactive Sites

In this work, we study the oscillatory behavior of CO oxidation in a catalyst constituted by Pd crystallites supported within a zeolite matrix by numerical simulation. For that, we perform a numerical bifurcation analysis of the STM (Sales−Turner−Maple) model (Sales, B. C.; Turner, J. E.; Maple, M. B. Surf. Sci.1982, 114, 381), which was modified by Basset and Imbihl (Bassett, M. R.; Imbihl, R. J. Chem. Phys.1990, 93, 811) and Slinko et al. (Slinko, M.; Kurkina, E.; Liauw, M.; Jaeger, N. J. Chem. Phys.1999, 111, 8105) to take into account subsurface oxygen, and we extend it to study the effect of diffusion; the final model is a mixed system with ordinary and partial differential equations. We study the influence of diffusion of one species along different directions and the effect of poisoning reaction sites. The bifurcation analysis identifies the fixed points and the kind of Hopf−Andronov bifurcation between oscillatory and steady state behavior. Our results show that as D is increased the amplitude and the period of oscillations are larger with respect to the homogeneous case and that there is a critical fraction of inert sites where the oscillations die and the transition from oscillatory to steady state corresponds to a Hopf bifurcation.

Time-on stream behavior of Pd-, Co-, and Mn-zeolite catalysts supported on metal blocks in high-temperature methane oxidation

Stability of the Pd-, Co-, and Mn-zeolite catalysts supported on metal blocks was studied in high-temperature methane oxidation. The temperature regions were found in which the starting catalysts exhibit stable performance. The temperature was determined at which a partial deactivation is followed by stabilization of catalysts in reaction environment. In terms of specific activity, the partially deactivated Pd-zeolite catalyst is several times more active than conventional oxidation catalysts Pd/Al2O3, Pt/Al2O3, and the most active oxide CeO·6Al2O3.

Direct Single-Stage Conversion of Synthesis Gas to Dimethoxymethane: Influence of the Sequence of Metal Introduction into Cu, Pd-Zeolite Catalysts on the Degree of Cu and Pd Reduction and Catalyst Acidity

The influence of the sequence of Cu and Pd introduction into zeolite matrice when preparing Cu, Pd-zeolite catalysts on their acidity and degree of metal reduction was studied. The mutual influence of Cu and Pd on their reducibility was analyzed. The selectivity of Cu, Pd-zeolite catalysts in conversion of synthesis gas to different products was elucidated.

Pd–Zeolites as Heterogeneous Catalysts in Heck Chemistry

Heck reactions were performed with 4-bromoacetophenone and n-butyl acrylate, yielding the trans-arylated acrylate ester with high selectivity. Pd–zeolite catalysts were compared with supported Pd metal catalysts. In order to obtain an active and heterogeneous catalyst, the preformed or in situ-formed catalytically active Pd0 species and the PdII intermediates must be sufficiently stabilized on the zeolites against leaching and against aggregation to inactive Pd black precipitates. The different states of Pd in the zeolites, i.e., Pd(NH3)42+, lattice-coordinated Pd2+ ions, PdO particles, and Pd0 metal particles of different sizes, were studied by a combination of diffuse reflectance UV–vis, XRD, SEM, and TEM before, during, and after catalytic reactions. The heterogeneous nature of the catalysis largely depends on the catalyst pretreatment and on the solvent and base used. With tributylamine as the base and in toluene, the Heck olefinations with Pd(NH3)42+–zeolites (0.4 wt% Pd; mordenite, Y, ZSM-5) and Pd0–mordenite (0.4 and 4 wt% Pd) are truly heterogeneous. Pd leaching from the zeolites, as evaluated in a very strict filtrate activity test, is clearly related to the presence of oxidized PdII in an all-oxygen environment, i.e., ionic Pd2+ or PdO. Supported Pd catalysts (Pd/C and Pd/SiO2) give rise to Pd leaching as well. The heterogeneous reactions with the zeolites can be accelerated by the addition of a quaternary ammonium salt promoter. In addition, the heterogeneous Heck catalysts can be applied in a continuous reactor.

Chaos and synchronisation in heterogeneous catalytic systems: CO oxidation over Pd zeolite catalysts

The influence of experimental parameters on the structure of global reaction rate oscillations and the coupling of local oscillators on a catalyst bed in a continuous stirred tank reactor is studied for the oxidation of CO on zeolite supported palladium catalysts. Global coupling can be achieved via mass transfer through the gas phase or via heat transfer in the case of a support of high heat conductivity. Characteristic differences in the activity of catalysts as well as in the period and the amplitude of the oscillations are related to the size of the palladium clusters and can be simulated by adding the state of the oxidation of the metal surface as a parameter to a common kinetic model. The analysis of observed chaotic behaviour leads to the conclusion that diffusional chaos characteristic of a distributed system is observed on the level of the zeolite crystallite that supports the palladium clusters.

The general mathematical model of CO oxidation reaction over Pd-zeolite catalyst

A new distributed mathematical model of reaction of CO oxidation over Pd-zeolite catalyst is presented. The model takes into account passing of the reactant flow through the catalyst layer, diffusion in pores of zeolite matrix, reaction on the surface of embedded Pd clusters, heat effect of the reaction, heat and mass transfer across the catalyst layer. Reaction on the Pd clusters is described by the new point model suggested herein. The model admits the existence of regular, chaotic and mixed-mode oscillations at the values of the parameters close to the experimental conditions.

Effect of the Acid-Base Properties of the Support on the Activity of Pd-Zeolite Catalysts for CO Oxidation

The effect of the acid-base properties of zeolite Y on the activity of palladium-zeolite catalysts for CO oxidation was studied. The modification of the support with basic additives was found to improve the cat- alyst activity. A linear correlation between the ratio between the amounts of O 2 and CO adsorbed on the surface of palladium and the catalyst activity was established.

Mathematical modeling of complex oscillatory phenomena during CO oxidation over Pd zeolite catalysts

A mathematical model, which simulates the complicated dynamic behavior experimentally observed during CO oxidation over Pd zeolite catalysts is presented. It describes the coupling of reaction rate oscillations, generated by various parts of the inhomogeneous catalytic layer through the gas phase. It can be shown, that the resulting dynamic behavior depends upon the difference between natural frequencies of local oscillators and the strength of coupling, which is defined mostly by the degree of conversion. Chaotic behavior could be identified under the condition of weak coupling for local oscillators with widely different natural frequencies. In the range of strong coupling the phenomenon of phase death has been obtained. A special type of intermittency chaos (“on–off” chaos) was observed in a small region of parameters under the conditions of strong coupling.

Effect of water vapor on the deactivation of Pd-zeolite catalysts for selective catalytic reduction of nitrogen monoxide by methane

For the selective reduction of nitrogen oxides (NOx) by methane, Pd-MOR (Pd: 0.47 wt.%) showed stable activity in the absence of water vapor at 450°C for more than 30 h, while it showed a gradual decrease in NOx conversion in the presence of water vapor. Pd-ZSM-5 (Pd: 0.58 wt.%) showed a gradual decrease in NOx conversion even in the absence of water vapor and almost lost activity in 20 h in the presence of water vapor. CO adsorption measurement revealed that Pd-ZSM-5 tested in the presence of water suffered the severest decrease in Pd dispersion. Raman measurement clearly indicated that PdO is formed on the deactivated samples. These results suggested that deactivation of Pd-zeolite is caused by Pd agglomeration to form PdO and water vapor promotes the agglomeration.

A mathematical model of oxidation of Co in a thin layer of a Pd zeolite catalyst

We construct and study a distributed mathematical model of oxidation ofCO in a planar layer of aPd zeolite catalyst. The model is a system of ordinary differential equations describing a chain of locally connected chemical oscillators. Each oscillator is an oscillatory process of the reaction occurring in the corresponding layer of zeolite. The peculiarity of this chain system is that the connection between the oscillators is parametric, since it is implemented through diffusion ofCO in the gaseous phase. We find conditions for existence and uniqueness of various types of oscillations in the system, including synchronous, quasi-periodic, and chaotic. We construct the phase diagram on the plane of two external parameters and give a bifurcation analysis, studying the scenario of transition to chaos. Two tables, 12 figures. Bibliography: 15 titles.

Dynamics of catalytic oscillators locally coupled through the gas phase

Mathematical model, describing the chain of locally coupled kinetic oscillators has been developed and analysed for the study of the influence of the internal diffusion upon the dynamic behaviour of a heterogeneous catalytic reaction rate. Kinetic oscillators represent spherical layers of a zeolite crystallite containing equal amounts of active metallic particles, where CO oxidation proceeds in an excess of oxygen in an oscillatory regime. Kinetic oscillators are locally coupled through the CO partial pressure, which is a control parameter for each uncoupled oscillator. The model was applied for the description of the complicated oscillations over Pd zeolite catalyst. The numerical and nonlinear analyses of the dynamic behaviour of the system, consisting of N coupled oscillators have been done. It was demonstrated that the decrease of the internal diffusion and the increase of the activity of each layer cause the greater strength of coupling. Various dynamic behaviour including regular periodic, quasiperiodic, mixed-mode and chaotic oscillations were found in the system depending upon the strength of coupling and CO partial pressure.

Oxidative interactions of propene with acetic acid on a Pd-zeolite catalyst

The interactions between C3H6, AcOH and O2 were investigated on 1.5 % Pd/TsVM catalysts prepared with and without addition of 15 % AcOK. Three states for surface oxygen on the promoted catalyst were distinguished. Two of them are involved in the oxidation of AcOH and C3H6 to CO2 and H2O, whereas the adsorbed species of the third type participates in the formation of allyl acetate. The O/Pd ratios for the promoted catalyst fall in the range from 3 to 4, the nonpromoted system is characterized by an O/Pd value of 0.5. IR-spectral data are used to discuss the reaction scheme for the formation of allyl acetate.

Iron or lanthanum promoters on the selectivity of palladium zeolites in methanol synthesis

The first example that demonstrates the distinct shift in selectivity towards methanol formation on the addition of Fe or La to Pd zeolite catalysts, together with enhanced activity, is reported.

The active forms of palladium in pd-zeolite catalysts for ethylene oligomerization

By studying the effects of preliminary treatment of Pd zeolites with various gases and investigating the x-ray photoelectron spectra of the zeolites themselves, it has been shown that it is the cationic form of the metal which is catalytically active in ethylene oligomerization. Metallic Pd is inactive in these catalysts under the conditions of the present work.

The isomerisation of n-hexane over molybdenum-containing catalysts

The isomerisation of n-hexane in the presence of unsupported molybdenum catalysts has been investigated. High surface area catalysts (⩾100 m 2 g −1) were prepared by the controlled reduction of molybdenum(VI) oxalate at temperatures below 773 K; low surface area catalysts were prepared by the controlled reduction of molybdenum dioxide at temperatures above 773 K. The extent of reduction was varied to give catalysts containing various proportions of Mo and MoO 2. The activity of the catalysts for the isomerisation of n-hexane was determined in a flow reactor ( T 603 K, P 1 atm ( about 1 × 10 5 N m −2), space velocity 1.0 (cm 3 hexane) (cm 3 catalyst) −1 h −1, H 2 C 6H 14 4.0 ). It was found that only those catalysts which contained both Mo metal and MoO 2 were active. The high surface area catalysts had activities which were comparable with the activity of a commercial Pd-Zeolite catalyst. A high selectivity for isomerisation (>98%) was observed for all the active catalysts.

Transformations of ethylene in presence of Pd-zeolite catalyst

1. The catalyst, obtained by inserting Pd into zeolite CaNaY by the ion exchange method, exhibits activity in the transformations of ethylene at 50–200°. 2. The condition for manifesting the maximum activity Is prior heat treatment of the catalyst with air. After treatment with hydrogen or helium the activity drops sharply at 100°.