Surface state during activation and reaction of high-performing multi-metallic alkyne hydrogenation catalysts

Bridier, Blaise; Pérez‐Ramírez, Javier; Knop‐Gericke, Axel; Schlögl, Robert; Teschner, Detre

doi:10.1039/c1sc00069a

Cited by 18 publications

(11 citation statements)

References 29 publications

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“…Bridier and Pérez‐Ramírez made use of the unselective character of Ni and Cu surfaces, engineering a Cu‐Ni‐Fe catalysts that showed full selectivity in propyne hydrogenation (Figure c) . In situ X‐ray absorption spectroscopy experiments demonstrated that Ni enhanced the surface H coverage and the reducibility of Fe and Cu, producing a well‐distributed Cu surface and hindering the catalyst re‐oxidation that would favor Fe segregation . Armbrüster et al .…”

Section: Advances In Catalyst Designmentioning

confidence: 99%

Advances in the Design of Nanostructured Catalysts for Selective Hydrogenation

et al. 2015

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Selective hydrogenations lay at the heart of many industrial processes. The archetypal catalysts for this class of reactions are generally prepared by ‘metal poisoning’ strategies: the active metal is protected and selectively deactivated with various compounds. This approach has been applied for decades, with limited understanding. Low product selectivity and presence of toxic elements in the catalyst pose severe constraints in the utilization of these materials in the future. Thus, to develop more sustainable catalysts, this field has recently gained momentum. This Review analyzes the concepts and frontiers that have been developed in the last decade: from nanostructuring less conventional metals in order to improve their ability to activate H2, to the use of oxides as active phases, from alloying, to the ensemble control in hybrid materials, and site isolation approaches in single‐site heterogeneous catalysts. Particular attention is given to the hydrogenation of alkynes and nitroarenes, two reactions at the core of the chemical industry, importantly applied in the manufacture of polymers, pharmaceuticals, nutraceuticals, and agrochemicals. The strategies here identified can be transposed to other relevant hydrogenations and can guide in the design of more advanced materials.

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Section: Advances In Catalyst Designmentioning

confidence: 99%

Advances in the Design of Nanostructured Catalysts for Selective Hydrogenation

et al. 2015

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“…Analysis of the XPD patterns of PdGa(1 1 1) and PdGa($\bar 1$ $\bar 1$ $\bar 1$ ) surfaces revealed the absence of surface segregation upon sputter and annealing cycles. Segregation of individual species to the surface has been observed on other multi‐metal hydrogenation catalysts to affect the selectivity pattern and complicate the analysis of the active and selective state of the catalyst 58. Despite the absence of segregation, more experimental effort was necessary to unambiguously determine the surface termination of the crystal under investigation.…”

Section: Single Crystal Surfaces Of Pdgamentioning

confidence: 99%

How to Control the Selectivity of Palladium‐based Catalysts in Hydrogenation Reactions: The Role of Subsurface Chemistry

et al. 2012

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Discussed are the recent experimental and theoretical results on palladium-based catalysts for selective hydrogenation of alkynes obtained by a number of collaborating groups in a joint multi-method and multi-material approach. The critical modification of catalytically active Pd surfaces by incorporation of foreign species X into the sub-surface of Pd metal was observed by in situ spectroscopy for X=H, C under hydrogenation conditions. Under certain conditions (low H2 partial pressure) alkyne fragmentation leads to formation of a PdC surface phase in the reactant gas feed. The insertion of C as a modifier species in the sub-surface increases considerably the selectivity of alkyne semi-hydrogenation over Pd-based catalysts through the decoupling of bulk hydrogen from the outmost active surface layer. DFT calculations confirm that PdC hinders the diffusion of hydridic hydrogen. Its formation is dependent on the chemical potential of carbon (reactant partial pressure) and is suppressed when the hydrogen/alkyne pressure ratio is high, which leads to rather unselective hydrogenation over in situ formed bulk PdH. The beneficial effect of the modifier species X on the selectivity, however, is also present in intermetallic compounds with X=Ga. As a great advantage, such PdxGay catalysts show extended stability under in situ conditions. Metallurgical, clean samples were used to determine the intrinsic catalytic properties of PdGa and Pd3Ga7. For high performance catalysts, supported nanostructured intermetallic compounds are more preferable and partial reduction of Ga2O3, upon heating of Pd/Ga2O3 in hydrogen, was shown to lead to formation of PdGa intermetallic compounds at moderate temperatures. In this way, Pd5Ga2 and Pd2Ga are accessible in the form of supported nanoparticles, in thin film models, and realistic powder samples, respectively

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“…The presence of Ni also found to hinder re-oxidation of the alloy constituents upon O 2 annealing. 60 The surface composition of Ni 65 Nb 35 polycrystalline alloy upon exposure to 1 bar of O 2 is temperature dependent. In particular, up to 373 K, Nb segregates and forms Nb 2 O 5 , while above 523 K segregation of nickel as a mixture of metal and oxide is observed.…”

Section: Single Feed Experimentsmentioning

confidence: 99%

Alloys in catalysis: phase separation and surface segregation phenomena in response to the reactive environment

Zafeiratos

Piccinin

Teschner

2012

Catal. Sci. Technol.

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Alloys play a crucial role in several heterogeneous catalytic processes, and their applications are expected to rise rapidly. This is essentially related to the vast number of configurations and type of surface sites that multi-component materials can afford. It is well established that the chemical composition at the surface of an alloy usually differs from that in the bulk. This phenomenon, referred to as surface segregation, is largely controlled by the surface free energy. However, surface energy alone cannot safely predict the active surface state of a solid catalyst, since the contribution of other parameters such as size and support effects, as well as influence of the adsorbates, play a major role. This can lead to numerous surface configurations as for example over the length of a catalytic reactor, as the chemical potential of the gas phase changes continuously over the catalyst bed and hence different reactions may prevail at different catalyst bed segments. Thanks to the rapid improvement of the analytical surface science characterization techniques and theoretical methodologies, the potential effects induced by alloyed catalysts are better understood. For catalysis, the relevance of measurements performed on well-defined surfaces under idealized ultrahigh vacuum conditions has been questioned and studies in environments that closely resemble conditions of working alloy catalysts are needed. In this review we focus on experimental and theoretical studies related to in situ (operando) observations of surface segregation and phase separation phenomena taking place on the outermost surface layers of alloy catalysts. The combination of first principles theoretical treatment and in situ observation opens up new perspectives of designing alloy catalysts with tailored properties

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Surface state during activation and reaction of high-performing multi-metallic alkyne hydrogenation catalysts

Cited by 18 publications

References 29 publications

Advances in the Design of Nanostructured Catalysts for Selective Hydrogenation

Advances in the Design of Nanostructured Catalysts for Selective Hydrogenation

How to Control the Selectivity of Palladium‐based Catalysts in Hydrogenation Reactions: The Role of Subsurface Chemistry

Alloys in catalysis: phase separation and surface segregation phenomena in response to the reactive environment

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