Palladium impregnation

In an automobile s catalytic converter, CO and hydrocarbons present in the exhaust gases are oxidized. Unfortunately the effectiveness of these units decreases with use. The phenomenon was studied by Summers and Hegedus in /. Catalysis, 51, 185 (1978) by means of an accelerated aging test on a palladium impregnated porous pellet packed bed converter. From the reported data on hydrocarbon conversion shown below, develop an expression to represent the deactivation rate of this catalyst. 

Standard analytical procedures, including CO chemisorption, indicated that the new charge appeared to be o the same quality as previously used catalyst. Subsequently, electron probe scans led to the observation that the depth of palladium impregnation had changed. A comparison of typical palladium penetrations for the two charges is shown in Table IV and in Figures 1 and 2. 

High yields of LFG or Isobutane and octane Improvement of the C5" fraction can be simultaneously obtained by hydrocracking raffinate over a palladium-Impregnated, nickel-substituted synthetic mlca-montmorlllonlte catalyst (0.7 wt % Pd-15 wt % Nl-SMM). A critical sulfur level of about 100 to 200 ppm In the feed Is essential to combine the features of desired product... 

K.C. Canon and J.J. Hacskaylo, Evaluation of palladium-impregnation on the performance of Vycor glass catalytic membrane reactor, J. Membr, ScL 65 259 (1992). 

For a good discussion of the Wacker-Smidt and related processes, see P. Wiseman, An Introduction to Industrial Organic Chemistry, Wiley New York, 1976, pp. 97-103. A process using palladium-impregnated silica, developed later, is superior to the homogeneously-catalyzed process described in equation 9.17. 

Experimental determination of Henry constants and adsorption hrat for various VOCs on faujasite type zeolites (NaY, HY and CsY with a Si/Al ratio of 2.4) and their Palladium impregnated form were adneved by a pulse chromatographic technique fixrm 448 to 623K for seven alkanes (linear, branched and cyclic probes) and fiom 523 to 673K for three aromatic compounds (toluene, m-xyloae and chlorobenzene). The Henry constant inoeases with the cation size and decreases if the zeolite is impregnate. 

Ahmad, A.L., M.A.T. Jaya, C.J.C. Derek, and M.A. Ahmad, Synthesis and characterization of TiOj membrane with palladium impregnation for hydrogen separation. Journal of Membrane Science, 2011.366(1-2) 166-175. 

To add surface area, the supports are uniformly coated with a slurry of gamma-alumina and recalcined under moderate conditions. The wash coat acts to accept the active metals, typically low levels of platinum and palladium, in a conventional impregnation process. In the United States in passenger car apphcations the spherical catalyst is used almost exclusively, and methods have been developed to replace the catalyst without removing the converter shell when vehicle inspection reveals that emission standards are not met. 

In this work, various conditions have been used for preparing catalysts to screening out a proper one mainly for CTA hydrogenation. The palladium precursor, impregnation time, calcination and reduction will be taken into account. 

CNF supported palladium calalysts Pd/CNFs) were prepared by wet impregnation. CNF was slurtiai in deionized water for about 15 min, and then foe palladium preeursor solution, which contained a desired amotmt of Pd (0.5 wt%), was titi ed to foe slurry. The latter was kept being agitated for a preset period of time, and foea filtaed (without washii and finally dried at about 120 Xi ovemi t. 

Two most firequently applied palladium precursor, H2PdCl4 and Pd(NH3)4Cl2, were usrf to prepare Pd/CNF by west impregnation. Results of foe CTA hydrogenation showed that under the same palladium loading ratio (0.5Pd%, see Table 2), foe Pd/CNF fi-om H2PdCl4... 

Preparation conditions of Pd/CNFs by wet impregnation method, such as palladium precursor, impregnation time, calcinations and reduction, are proved to have profound effect on the catalytic property. The catalyst prqjared by impregnating HzPdCLi precursor in an hour, then calcinated in air and reduced in 20%H2/Ar is believed to perform better in CTA hydropurification than the industrial Pd/C under laboratory conditions. 

Platinum catalysts were prepared by ion-exchange of activated charcoal. A powdered support was used for batch experiments (CECA SOS) and a granular form (Norit Rox 0.8) was employed in the continuous reactor. Oxidised sites on the surface of the support were created by treatment with aqueous sodium hypochlorite (3%) and ion-exchange of the associated protons with Pt(NH3)42+ ions was performed as described previously [13,14]. The palladium catalyst mentioned in section 3.1 was prepared by impregnation, as described in [8]. Bimetallic PtBi/C catalysts were prepared by two methods (1) bismuth was deposited onto a platinum catalyst, previously prepared by the exchange method outlined above, using the surface redox reaction ... 

Second, following a cleaning procedure with formalin, wet-chemical impregnation with palladium was performed [17]. The micro channels were exposed to a solution of 200 mg of PdCl2 in 40 ml of distilled water for 5 h. The PdCl2 was reduced to elemental Pd by formalin still present in the nanopores of the oxide layer which were generated one step before. This was followed by calcination. 

Figure 2 schematically presents a synthetic strategy for the preparation of the structured catalyst with ME-derived palladium nanoparticles. After the particles formation in a reverse ME [23], the hydrocarbon is evaporated and methanol is added to dissolve a surfactant and flocculate nanoparticles, which are subsequently isolated by centrifugation. Flocculated nanoparticles are redispersed in water by ultrasound giving macroscopically homogeneous solution. This can be used for the incipient wetness impregnation of the support. By varying a water-to-surfactant ratio in the initial ME, catalysts with size-controlled monodispersed nanoparticles may be obtained. 

The material being impregnated by the palladium precursor, once all the internal exchanged positions have been already occupied by Co2+, PdO is formed on the external surface of the zeolite grain, as observed by TEM (not shown, [12]). 

It was prepared by incipient wetness impregnation using Pd(NH3)4Cl2. The sample was then dried at 573 K (300°C) and subsequently calcined at 773 K (500°C) under synthetic air. The amount of palladium introduced was 0.5wt.%. 

The structure of the metal particles dispersed on a silica powder support ( Aerosil 380, 70 A average silica particle diameter) has been studied by Avery and Sanders (47) using electron microscopy in both bright and dark field, to determine the extent to which the metal particles were multiply twinned or of ideal structure. Platinum, palladium, and gold were examined. These catalysts were prepared by impregnation using an aqueous solution of metal halide derivatives, were dried at 100°-150°C, and were hydrogen... 

The Pd-ZSM-5 catalysts are prepared by impregnation and by solid exchange methods on the carrier of HZSM-5 and NaZSM-5 (Si/Al = 26) with variable palladium loading and different pre-treatment gas (He and O2). N2-physisorption, DRX and CH4-TPR are the main techniques used to characterise these catalysts. Furthermore, total methane oxidation is used to test their catalytic activity. Among the preparative variables, the solid exchange method, the NaZSM-5 support and the increase of the palladium loading improve considerably the activity of the Pd-ZSM-5 catalysts in methane oxidation. 

Keywords Total methane oxidation, Pd-ZSM-5 catalysts, impregnation, solid exchange method, pre-treatment and palladium loading. 

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