Palladium Supported on Alumina Catalysts Prepared by MOCVD and Impregnation Methods

Abstract

Conventional MOCVD method has been explored to prepare Pd supported catalysts. Pd and PdO phases were found on the surface of the support. Small Pd particles about 1 to 3 nm and dispersions up to 19%were obtained by MOCVD. TPR results indicated that several surface Pd compounds are reduced. At temperatures below 25°C, PdO, the main compound, is completely converted to metallic Pd which forms hydrides. At higher temperatures, between 500 to 800°C, the reduction peaks could be attributed to Pd-support interactions and a strong support dehydroxylation. All catalysts were inactive in benzene hydrogenation and a significant conversion was only detected a temperatures above 100 °C. This was explained by the reduced accessibility of Pd sites imposed by the carbon contamination and by the Pd-Al2O3 interactions.

Hydrodehalogenation of haloarenes over Silica supported Pd and Ni

“…There is an apparent discrepancy in the literature concerning the TPR response of supported Pd that is compounded by incomplete procedural descriptions and a mismatch in terms of sample pretreatment prior to TPR. While it has been reported that PdO reduction on SiO 2 and Al 2 O 3 supports takes place at room temperature [84][85][86], H 2 consumption peaks up to 523 K have also been reported [80,87,88]. The appearance of a positive TPR peak in the Pd/SiO 2 profile shown in Fig.…”

Palladium supported on structured and nonstructured carbon: A consideration of Pd particle size and the nature of reactive hydrogen

“…2; repeated TPR runs are included to illustrate the level of reproducibility. All the TPR profiles are characterized by a single negative peak at 382 ± 6 K. A search through the literature has unearthed an array of TPR profiles for carbon supported Pd that exhibit the sole appearance of positive (H 2 consumption) [11,25,26,33,34,[36][37][38][50][51][52][53] or negative (H 2 production) [6,25,26,34,35,38,53,54] peaks or a combination of both [35,36,38,55]. In a series of blank runs, there was no observable H 2 consumption or release by/from the carbon supports over the same temperature range.…”

“…None of the Pd systems (bulk/physically mixed/chemically supported) considered in this work generated a positive peak during TPR in advance of H 2 release. There is some consensus in the literature that the reduction of supported [33,35,51,55,58,59] and unsupported PdO [58,60] occurs at room temperature. It should, however, be noted that Nag [25] generated a TPR profile that suggested reduction of PdO supported on carbon at two different temperatures (318 and 345 K).…”

Chemical Vapor Deposition of Iridium, Platinum, Rhodium and Palladium

“…[87][88][89][90][91][92] For instance, a uniform distribution of palladium insidealumina pores (3-6 nm in diameter) was completed by decomposition of Pd(acac) 2 without assistance of a reactive gas. 90) In this case, palladium could be in the form of ultrafine particles as suggested by the broadening of its XRD reflections.…”

“…64,65,102) The use of oxygen is also effective to achieve high-purity palladium films (>99 mass%Pd) from this complex. 91,108) On the other hand, Pd(Me allyl)(hfac) and Pd(Me allyl)(acac) may also produce high-purity palladium films but exclusively with the assistance of oxygen gas. 108) Films prepared in hydrogen containing atmosphere or in vacuum show significant carbon contamination (15-40 mass%C).…”