Development of highly active and selective novel Pd based acetoxylation catalysts and prevention of catalyst deactivation by Bi modification

Benhmid, A.; Narayana, K.V.; Martin, Andreas; Lücke, Bernhard; Pohl, Marga‐Martina

doi:10.1039/b410310f

Cited by 14 publications

(14 citation statements)

References 9 publications

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“…The unexpected catalytic activity of tri-metal PtPdBi nanowires may have originated from the synergistic effect of the three elements: either Pd or Bi alloyed with Pt can efficiently This journal is © The Royal Society of Chemistry 2014 enhance the catalytic activity of Pt and therefore make a separate contribution to the improvement of catalytic performance of PtPdBi nanowires. 51 The performance improvement of the composite catalyst was attributed to electronic, or geometric effects, or a combination of both. 52 The geometric effect refers to a simple surface site-access blockage of a desired active site in the case of poisoning or of a poison-generating site in the case of the promotion, sometimes called the "third body effect".…”

Section: Catalytic Activity Of Ptpdbi Nanowiresmentioning

confidence: 99%

“…Therefore, the geometric effect should not be a dominant factor. The catalytic activity of PtPdBi nanowires should therefore be attributed to the electronic effects arising from alternations of electron density near the Fermi level because of the structural strain caused by the doping of Bi, 51 that provides new active sites on which p-nitrophenol is reduced more easily than with PtPd. 51,53 Another question is if the shape of the PtPdBi nanowire contributes to its catalytic activity?…”

Section: Catalytic Activity Of Ptpdbi Nanowiresmentioning

confidence: 99%

“…The catalytic activity of PtPdBi nanowires should therefore be attributed to the electronic effects arising from alternations of electron density near the Fermi level because of the structural strain caused by the doping of Bi, 51 that provides new active sites on which p-nitrophenol is reduced more easily than with PtPd. 51,53 Another question is if the shape of the PtPdBi nanowire contributes to its catalytic activity? In electrocatalytic reactions, if nanowires have the same components as nanospheres, the former are able to exhibit better performance than the latter, which has been attributed to good conductivity of nanowires.…”

Section: Catalytic Activity Of Ptpdbi Nanowiresmentioning

confidence: 99%

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Synthesis of ultrathin PtPdBi nanowire and its enhanced catalytic activity towards p-nitrophenol reduction

et al. 2014

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Ultrathin PtPdBi tri-metallic nanowires (NWs, diameters ranged from 3 nm to 5 nm) were prepared in a onepot polyol process in which the molar ratios of the three metals could be tuned depending on the amount of initial precursors. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and elemental mapping revealed that these NWs were alloys with a face-centered cubic crystal structure similar to PtPd alloy. p-Nitrophenol was used as a probe to assess the catalytic activities of the as-prepared PtPdBi NWs. The results indicated that the existence of a small amount of Bi in the PtPdBi alloy efficiently improved its catalytic capability towards the reduction of p-nitrophenol. At the specified Pt : Pd : Bi ratio of 55 : 38 : 7, PtPdBi nanowires showed the best catalytic activity of all the nanomaterials tested (Pt, Pd and PdPd spherical nanoparticles; PtBi and PdBi nanowires) a feature that was attributed to the optimal synergistic effect of the three metallic elements.

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Section: Catalytic Activity Of Ptpdbi Nanowiresmentioning

confidence: 99%

Section: Catalytic Activity Of Ptpdbi Nanowiresmentioning

confidence: 99%

Section: Catalytic Activity Of Ptpdbi Nanowiresmentioning

confidence: 99%

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Synthesis of ultrathin PtPdBi nanowire and its enhanced catalytic activity towards p-nitrophenol reduction

et al. 2014

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“…To achieve this objective, we modified the composition of the Pd-Sb/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.…”

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confidence: 99%

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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“…5 However, recently a remarkable breakthrough has been achieved in the synthesis of benzyl acetate (BA) via gas-phase acetoxylation of toluene with O 2 using Pd/TiO 2 catalysts promoted with Sb, Bi or Cu. [6][7][8][9][10][11][12] The highest catalytic performance was obtained with a catalyst consisting of 10 wt% Pd and 8 wt% Sb supported on anatase, which reached a maximum BA selectivity of 86% at a toluene conversion of 90%. 8 The striking drawbacks of this catalyst were a long conditioning time of about 10 h and fast deactivation.…”

Section: Introductionmentioning

confidence: 99%

Tailoring the synthesis of supported Pd catalysts towards desired structure and size of metal particles

Gatla

Radnik

Kalevaru

et al. 2010

Phys. Chem. Chem. Phys.

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In a systematic study, the influence of different preparation parameters on phase composition and size of metal crystallites and particles in Pd-Cu/TiO(2) and Pd-Sb/TiO(2) catalyst materials has been explored. Temperature and atmosphere of thermal pretreatment (pure He or 10% H(2)/He), nature of metal precursors (chlorides, nitrates or acetates) as well as of ammonium additives (ammonium sulfate, nitrate, carbonate) and urea were varied with the aim of tailoring the synthesis procedure for the preferential formation of metal particles with similar size and structure as observed recently in active catalysts after long-term equilibration under catalytic reaction conditions in acetoxylation of toluene to benzylacetate. Among the metal precursors and additives, the chloride metal precursors and (NH(4))(2)SO(4) were most suitable. Upon thermal pretreatment of Pd-Sb or Pd-Cu precursors, chloroamine complexes of Pd and Cu are formed, which decompose above 220 degrees C to metallic phases independent of the atmosphere. In He, metallic Pd particles were formed with both the co-components. In H(2)/He flow, Pd-Cu precursors were converted to core-shell particles with a Cu shell and a Pd core, while Sb(1)Pd(1) and Sb(7)Pd(20) alloy phases were formed in the presence of Sb. Metal crystallites of about 40 nm agglomerate to particles of up to 150 nm in He and to even larger size in H(2)/He.

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Development of highly active and selective novel Pd based acetoxylation catalysts and prevention of catalyst deactivation by Bi modification

Abstract: A first approach to successful prevention of catalyst deactivation while simultaneously achieving extremely high selectivity of benzyl acetate (> or = 95%) at significantly high toluene conversion (> 70%) by gas phase acetoxylation over novel Pd-Sb-Bi/TiO2 catalysts.

Cited by 14 publications

References 9 publications

Synthesis of ultrathin PtPdBi nanowire and its enhanced catalytic activity towards p-nitrophenol reduction

Synthesis of ultrathin PtPdBi nanowire and its enhanced catalytic activity towards p-nitrophenol reduction

Deactivation of Pd Acetoxylation Catalysts: Direct Observations by XPS Investigations

Tailoring the synthesis of supported Pd catalysts towards desired structure and size of metal particles

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