Highly efficient Pd?Sb?TiO catalysts for the vapour phase acetoxylation of toluene to benzyl acetate

Benhmid, A.; Narayana, K.V.; Martin, Andreas; Lücke, Bernhard; Bischoff, Stefan; Pohl, Marga‐Martina; Radnik, Jörg; Schneider, Mat­thias

doi:10.1016/j.jcat.2004.12.019

Cited by 20 publications

(28 citation statements)

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“…[7][8][9] Vapor-phase processes were previously not successful in terms of obtaining higher yields of BA with acceptable time-on-stream stability of the catalysts. [10,11] However, the recently developed Pd-Sb/TiO 2 catalysts [12][13] displayed remarkably higher conversion of toluene (> 90 %) and yields of BA (> 75 %) with a space-time yield of up to 700 g kg À1 h …”

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Deactivation of Pd Acetoxylation Catalysts: Direct Observations by XPS Investigations

et al. 2005

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Catalyst deactivation is a problem of great concern in industrial catalytic processes. Hence, prevention of catalyst deactivation poses substantial challenges in the design and operation of large-scale catalytic processes. The usual way to overcome the deactivation problem is to modify the catalyst composition by using different promoters. Although various promoters have been used for different oxidation reactions, [1][2][3][4] their precise role is not known. Unfortunately, most of the interpretations on the role of promoters are rather hypothetical probably owing to the lack of information about the exact surface structure. Among the known promoters, bismuth has very attractive properties as a promoting element in numerous heterogenous oxidation catalysts, particularly in association with noble metals. [1][2][3][4][5][6] However, the origin of the promoting role of Bi is still a matter of discussion.Acetoxylation is an industrially important reaction for producing esters in a single step. Benzyl acetate (BA), the desired product from acetoxylation of toluene, is widely used in the food, perfumery, and chemical industries. Most of the work reported so far on the acetoxylation of toluene is confined to liquid-phase and batch reactors. [7][8][9] Vapor-phase processes were previously not successful in terms of obtaining higher yields of BA with acceptable time-on-stream stability of the catalysts. [10,11] However, the recently developed Pd-Sb/TiO 2 catalysts [12][13] displayed remarkably higher conversion of toluene (> 90 %) and yields of BA (> 75 %) with a space-time yield of up to 700 g kg À1 h À1. To our knowledge, this is the best result reported so far under gas-phase conditions. However, these catalysts are observed to undergo deactivation readily after several hours of operation as a result of coke deposits, which obviously hampers their application on a commercial scale.Considering the limited lifetime of these catalysts, we have directed our research efforts to develop stable and novel Pd compounds that have improved catalyst lifetime as well as the higher activity and selectivity of the earlier catalysts. To achieve this objective, we modified the composition of the PdSb/TiO 2 catalysts by adding promoters such as Bi, Cu, and Sn. [14][15] Among these promoters, the Bi modification improved both the catalyst life as well as the selectivity for desired product (BA). However, the precise role of Bi remained unclear. In the present study we examine the catalyst deactivation phenomenon of Pd-Sb/TiO 2 catalysts and the role of Bi in improving catalyst lifetime and selectivity.In the earlier investigations on Pd-Sb/TiO 2 catalysts [13] we clearly detected differences between the fresh and used catalysts. The used catalysts displayed drastic increase in Pd particle size, coke deposition, loss of both Pd and Sb at the surface etc. In view of this, a TiO 2 -supported catalyst with 10 wt % Pd and 8 wt % Sb was then chosen as a model catalyst (designated as 10Pd8Sb) and subjected to reaction conditions for a wide ran...

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Deactivation of Pd Acetoxylation Catalysts: Direct Observations by XPS Investigations

et al. 2005

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“…Despite achieving an acceptably higher conversion of toluene and high yield of BA, the catalyst samples were observed to suffer from the problem of easy catalyst deactivation. The analysis of coke in the spent (deactivated) samples indicated that the deactivation was due to carbon deposits during the course of the reaction [79]. The amount of coke deposition was observed to increase with increasing Pd load.…”

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Bimetallic Catalysts Containing Gold and Palladium for Environmentally Important Reactions

2016

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Supported bimetallic nanoparticles (SBN) are extensively used as efficient redox catalysts. This kind of catalysis particularly using SBN has attracted immense research interest compared to their parent metals due to their unique physico-chemical properties. The primary objective of this contribution is to provide comprehensive overview about SBN and their application as promising catalysts. The present review contains four sections in total. Section 1 starts with a general introduction, recent progress, and brief summary of the application of SBN as promising catalysts for different applications. Section 2 reviews the preparation and characterization methods of SBN for a wide range of catalytic reactions. Section 3 concentrates on our own results related to the application of SBN in heterogeneous catalysis. In this section, the oxidation of cyclohexane to adipic acid (an eco-friendly and novel approach) will be discussed. In addition, the application of bimetallic Pd catalysts for vapor phase toluene acetoxylation in a fixed bed reactor will also be highlighted. Acetoxylation of toluene to benzyl acetate is another green route to synthesize benzyl acetate in one step. Finally, Section 1 describes the summary of the main points and also presents an outlook on the application of SBN as promising catalysts for the production of valuable products.

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“…Der zweite Schritt umfasste die Imprägnierung mit der gewünschten Menge an PdCl 2 und anschließen-des Trocknen (120 8C, 16 h). Die ausführliche Vorgehensweise für die Katalysatorpräparation, [16] die Auswahl der Katalysatoren und die Produktanalyse sind schon beschrieben worden. [13] Die XPS-Messungen wurden an einem VG ESCALAB220iXL mit Al Ka -Strahlung, die TEM-Analysen mit einem Philips CM20 (twin) bei 200 kV mit einem EDAX PV9900 (energieauflösende Röntgenspektroskopie) durchgeführt.…”

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“…Die meisten Arbeiten über die Acetoxylierung von Toluol beschränkten sich auf die Flüssigphase und Batch-Reaktoren, [7][8][9] wohingegen Gasphasenprozesse bei einer ausreichenden Zeitstabilität der Katalysatoren im Gasstrom bisher keine zufriedenstellenden BAAusbeuten lieferten. [10,11] Die kürzlich entwickelten PdSb/ TiO 2 -Katalysatoren [12][13] Wichtige Effekte der Bi-Zugabe sind 1) die hohe BASelektivität (> 95 %) und 2) die Lösung des Problems der Katalysatordesaktivierung. Abbildung 1 vergleicht die katalytischen Merkmale von 10Pd8Sb mit und ohne Bi während der Zeit im Reaktantgasstrom.…”

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“…Der Anstieg des Toluolumsatzes wurde auf eine Größenzu-nahme der Pd-Partikel während der Reaktion zurückgeführt, wohingegen die Abnahme der katalytischen Aktivität mit der zunehmenden Koksablagerung erklärt wurde. [13] Das Wachstum der Pd-Partikel bis zu einer kritischen Größe war mit TEM eindeutig zu beobachten. Danach bleibt die Größe der Teilchen mehr oder weniger konstant, während die katalyti- Röntgenbeugung lieferte keine Hinweise auf die Bildung von kristallinen intermetallischen Phasen zwischen Pd und Bi, wie sie aus der Literatur bekannt sind.…”

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Desaktivierung von Pd‐Katalysatoren zur Acetoxylierung: direkte Beobachtung durch XPS‐Untersuchungen

et al. 2005

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Highly efficient Pd?Sb?TiO catalysts for the vapour phase acetoxylation of toluene to benzyl acetate

Cited by 20 publications

References 20 publications

Deactivation of Pd Acetoxylation Catalysts: Direct Observations by XPS Investigations

Deactivation of Pd Acetoxylation Catalysts: Direct Observations by XPS Investigations

Bimetallic Catalysts Containing Gold and Palladium for Environmentally Important Reactions

Desaktivierung von Pd‐Katalysatoren zur Acetoxylierung: direkte Beobachtung durch XPS‐Untersuchungen

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