Volcano Relations for Oxidation of Hydrogen Halides over Rutile Oxide Surfaces

Toftelund, Anja; Man, Isabela Costinela; Hansen, Heine Anton; Abild‐Pedersen, Frank; Bligaard, Thomas; Studt, Felix

doi:10.1002/cctc.201200140

ChemCatChem

2012

DOI: 10.1002/cctc.201200140

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Volcano Relations for Oxidation of Hydrogen Halides over Rutile Oxide Surfaces

Anja Toftelund

Isabela Costinela Man

Heine Anton Hansen

et al.

Abstract: We investigate the heterogeneously catalysed oxidation of HX (X=Cl, Br and I) on the RuO2 (1 1 0) surface with DFT. We also solve a micro‐kinetic model of HX oxidation and compare oxidation activity at different coverages. We further establish linear energy relations for the reaction intermediates over a range of different rutile oxide surfaces. Based on the scaling relations, two descriptors are identified that describe the reactions uniquely. By combining scaling with the micro‐kinetic model, activity volcan… Show more

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Cited by 13 publications

(22 citation statements)

References 30 publications

(43 reference statements)

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“…Toftelund et al [9] conducted the first theoretical study by using DFT to compare hydrogen halide oxidations over defect-free rutile-type oxides and by selecting the oxygen dissociation energy as the descriptor of catalytic activity. In line with our experimental results, RuO 2 was identified as the most active material in HBr oxidation.…”

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confidence: 99%

Catalytic Bromine Recovery: An Enabling Technology for Emerging Alkane Functionalization Processes

Moser¹,

Rodríguez-García²,

Amrute³

et al. 2013

ChemCatChem

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The functionalization of light alkanes into value-added products represents one of the most relevant and challenging areas in catalysis research. [1] In particular, energy-efficient and costeffective processes to selectively convert the abundant reserves of natural gas into chemical intermediates and fuels are highly sought. Pioneering work by Olah et al. [2] and more recent studies by McFarland, Stucky, and co-workers [3,4] have shown that the bromination of light alkanes to the corresponding alkyl bromides followed by a catalyzed elimination reaction offers an attractive route to obtain a broad spectrum of desirable products (Figure 1). Bromine-mediated reactions of hydrocarbons are far more selective and occur under much milder conditions (typically 475 K and 100-200 kPa) than classical alkane upgrading processes (steam reforming, steam cracking, and dehydrogenation), which leads to increased product yields, energy savings, and decreased CO 2 emissions.[3] For instance, the conversion of methane into olefins through methyl bromide represents an intensified alternative to the conventional methanol-based process by circumventing the costly intermediate syntheses of syngas and methanol.[4c] Another illustrative example comprises the bromine-based dehydrogenation of propane, which gives a yield of propylene that is three higher than the highest reported yields given by oxidative dehydrogenation.[4e] However, as shown in Figure 1, every mole of alkane converted through this two-step process generates two moles of HBr byproduct. Accordingly, the development of a robust and economic process to recover Br 2 from HBr is essential to enable the sustainable bromine-mediated upgrading of alkanes. A suitable halogen regeneration technology would also aid the valorization of waste HBr streams originating from the manufacture of organobromides employed as flame retardants, polymers, and pharmaceutical intermediates. [5] Bromine recovery can be achieved by HBr electrolysis, [6] HBr oxidation, [5, 7] and HBr absorption by a cataloreactant followed by its reoxidation. [4a,b] To our knowledge, none of these processes are established on a technical scale. The catalyzed gasphase oxidation of HBr with O 2 or air (2 HBr) is particularly attractive owing to its low energy requirement and the relative simplicity of the process. Nonetheless, the identification of highly active and stable catalysts can be anticipated as critical owing to the exothermic and corrosive nature of the reaction. Different materials have been patented, [5] of which supported cerium-based compounds are the most prominent.[7] However, the absence of systematic studies aimed at screening the performance of potential candidates and the limited understanding of the reaction mechanism have hindered the design of suitable HBr oxidation catalysts and their large-scale implementation. Herein, we introduce several efficient heterogeneous catalysts for this reaction that enable bromine recovery at relatively low temperatures. These catalytic materials will improve th...

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mentioning

confidence: 99%

Catalytic Bromine Recovery: An Enabling Technology for Emerging Alkane Functionalization Processes

Moser¹,

Rodríguez-García²,

Amrute³

et al. 2013

ChemCatChem

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show abstract

“…The catalyzed oxidation of HBr is tightly related to the Deacon reaction 5. 6 Experiments have identified the outstanding performance of RuO 2 for the oxidation of HX (X=Cl, Br) 5. In fact, computational screening based on density functional theory (DFT) have indicated that the closest point to the maximal activity for rutile materials is RuO 2 6.…”

mentioning

confidence: 99%

“…6 Experiments have identified the outstanding performance of RuO 2 for the oxidation of HX (X=Cl, Br) 5. In fact, computational screening based on density functional theory (DFT) have indicated that the closest point to the maximal activity for rutile materials is RuO 2 6. However, ruthenium‐based catalysts present a clear drawback for a widespread implementation owing to ruthenium’s relatively high and fluctuating price.…”

mentioning

confidence: 99%

“…For example, stoichiometric TiO 2 was predicted to deliver a 10‐order of magnitude lower reaction rate than RuO 2 . The highly endergonic nature of oxygen dissociation over defect‐free TiO 2 rutile was put forward as the reason for its inactivity 6. Indeed theoretical studies have shown that the surface of stoichiometric TiO 2 is unable to dissociatively adsorb O 2 6.…”

mentioning

confidence: 99%

“…The highly endergonic nature of oxygen dissociation over defect‐free TiO 2 rutile was put forward as the reason for its inactivity 6. Indeed theoretical studies have shown that the surface of stoichiometric TiO 2 is unable to dissociatively adsorb O 2 6. 7 Several authors7 have identified that the adsorption of O 2 can be ‘switched on’ provided that oxygen vacancies exist in the material.…”

mentioning

confidence: 99%

See 2 more Smart Citations

The Virtue of Defects: Stable Bromine Production by Catalytic Oxidation of Hydrogen Bromide on Titanium Oxide

et al. 2014

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Rutile TiO2 is a heavily investigated oxide with, to date, scarce applications in industrial catalysis. The inactivity of this material in oxidations has been related to its inability to dissociate molecular oxygen. Herein we show how rutile catalyzes the oxidation of HBr to Br2 through defect states that are introduced during the reaction. The identification of active, stable, and abundant materials for bromine production is key to the future implementation of Br2‐mediated alkane functionalization processes. The catalytic properties of TiO2 are discussed in comparison to expensive rutile‐type oxides, such as RuO2 and IrO2, on the basis of surface characterization and molecular modeling.

show abstract

The Virtue of Defects: Stable Bromine Production by Catalytic Oxidation of Hydrogen Bromide on Titanium Oxide

et al. 2014

View full text Add to dashboard Cite

Rutile TiO2 is a heavily investigated oxide with, to date, scarce applications in industrial catalysis. The inactivity of this material in oxidations has been related to its inability to dissociate molecular oxygen. Herein we show how rutile catalyzes the oxidation of HBr to Br2 through defect states that are introduced during the reaction. The identification of active, stable, and abundant materials for bromine production is key to the future implementation of Br2-mediated alkane functionalization processes. The catalytic properties of TiO2 are discussed in comparison to expensive rutile-type oxides, such as RuO2 and IrO2, on the basis of surface characterization and molecular modeling.

show abstract

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Volcano Relations for Oxidation of Hydrogen Halides over Rutile Oxide Surfaces

Cited by 13 publications

References 30 publications

Catalytic Bromine Recovery: An Enabling Technology for Emerging Alkane Functionalization Processes

Catalytic Bromine Recovery: An Enabling Technology for Emerging Alkane Functionalization Processes

The Virtue of Defects: Stable Bromine Production by Catalytic Oxidation of Hydrogen Bromide on Titanium Oxide

The Virtue of Defects: Stable Bromine Production by Catalytic Oxidation of Hydrogen Bromide on Titanium Oxide

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