Mechanisms governing selective hydrogenation of acetylene over γ-Mo2N surfaces

Zainab N. Jaf, Mohammednoor Altarawneh, Hussein A. Miran, Zhong Tao Jiang, Bogdan Z. Dlugogorski

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Selective hydrogenation of acetylene (ethyne), present in hydrocarbon feed into ethylene (ethene) plays critical importance in processing operations. Unsupported molybdenum-nitride (Mo2N) catalysts mediate surface hydrogenation of ethyne with a profound selectivity, similar to that observed over noble metals. However, the underlying mechanisms governing the H2-C2H2-Mo2N interaction leading to partial, rather than complete, hydrogenation remain largely unclear. In this contribution, we have found that molecular hydrogen adopts several physisorbed states prior to its dissociation, mainly on 3-fold hollow fcc (H1) and 4-fold hollow fcc (H3) sites over the (111) and (100) terminations of γ-Mo2N, respectively. Our results on the interaction of hydrogen with the γ-Mo2N surface concur very well with the analogous experimental findings of the dissociation occurring preferentially on the vacant nitrogen sites, the mobility of surface-adsorbed hydrogen atoms from weak to strong adsorption sites (associated with pathways of low and high activation energies for dissociation of adsorbed H2 on the catalyst surface) and the inhibition effect of pre-adsorbed oxygen on H2 dissociation. The constructed reaction mechanism, the estimated reaction rate constants, and the micro-kinetic modelling explain the selective hydrogenation of ethyne into ethene, rather than ethane. We demonstrate that the occurrence of selective hydrogenation rests on two aspects: distinctive energy profiles of the hydrogenation steps in partial versus full hydrogenation routes and thermodynamic selectivity entailing higher surface stability of adsorbed C2H2 in comparison to C2H4. Higher stabilities of the adsorbed open-shell CxHy species (C2H3∗, C2H5∗) on the (100) surface, in comparison to those on the (111) surface, indicate increased tendency for oligomerisation to occur on the (100) surface. Thermo-kinetic parameters reported herein provide molecular-level understanding of the unique and highly selective hydrogenation capacity of the γ-Mo2N catalysts. Such knowledge is critically important in designing optimum operational conditions for practical processing operations.

Original languageEnglish
Pages (from-to)943-960
Number of pages18
JournalCatalysis Science and Technology
Volume7
Issue number4
DOIs
Publication statusPublished - 1 Jan 2017
Externally publishedYes

Fingerprint

Acetylene
Hydrogenation
Hydrogen
Catalysts
Ethylene
Oligomerization
Ethane
Molybdenum
Precious metals
Processing
Hydrocarbons
Kinetic parameters
Nitrides
Reaction rates
Rate constants
Nitrogen
Activation energy
Thermodynamics
Oxygen
Adsorption

Cite this

Jaf, Z. N., Altarawneh, M., Miran, H. A., Jiang, Z. T., & Dlugogorski, B. Z. (2017). Mechanisms governing selective hydrogenation of acetylene over γ-Mo2N surfaces. Catalysis Science and Technology, 7(4), 943-960. https://doi.org/10.1039/c6cy02110g
Jaf, Zainab N. ; Altarawneh, Mohammednoor ; Miran, Hussein A. ; Jiang, Zhong Tao ; Dlugogorski, Bogdan Z. / Mechanisms governing selective hydrogenation of acetylene over γ-Mo2N surfaces. In: Catalysis Science and Technology. 2017 ; Vol. 7, No. 4. pp. 943-960.
@article{437967f2465d411697761e44fd6e0f62,
title = "Mechanisms governing selective hydrogenation of acetylene over γ-Mo2N surfaces",
abstract = "Selective hydrogenation of acetylene (ethyne), present in hydrocarbon feed into ethylene (ethene) plays critical importance in processing operations. Unsupported molybdenum-nitride (Mo2N) catalysts mediate surface hydrogenation of ethyne with a profound selectivity, similar to that observed over noble metals. However, the underlying mechanisms governing the H2-C2H2-Mo2N interaction leading to partial, rather than complete, hydrogenation remain largely unclear. In this contribution, we have found that molecular hydrogen adopts several physisorbed states prior to its dissociation, mainly on 3-fold hollow fcc (H1) and 4-fold hollow fcc (H3) sites over the (111) and (100) terminations of γ-Mo2N, respectively. Our results on the interaction of hydrogen with the γ-Mo2N surface concur very well with the analogous experimental findings of the dissociation occurring preferentially on the vacant nitrogen sites, the mobility of surface-adsorbed hydrogen atoms from weak to strong adsorption sites (associated with pathways of low and high activation energies for dissociation of adsorbed H2 on the catalyst surface) and the inhibition effect of pre-adsorbed oxygen on H2 dissociation. The constructed reaction mechanism, the estimated reaction rate constants, and the micro-kinetic modelling explain the selective hydrogenation of ethyne into ethene, rather than ethane. We demonstrate that the occurrence of selective hydrogenation rests on two aspects: distinctive energy profiles of the hydrogenation steps in partial versus full hydrogenation routes and thermodynamic selectivity entailing higher surface stability of adsorbed C2H2 in comparison to C2H4. Higher stabilities of the adsorbed open-shell CxHy species (C2H3∗, C2H5∗) on the (100) surface, in comparison to those on the (111) surface, indicate increased tendency for oligomerisation to occur on the (100) surface. Thermo-kinetic parameters reported herein provide molecular-level understanding of the unique and highly selective hydrogenation capacity of the γ-Mo2N catalysts. Such knowledge is critically important in designing optimum operational conditions for practical processing operations.",
author = "Jaf, {Zainab N.} and Mohammednoor Altarawneh and Miran, {Hussein A.} and Jiang, {Zhong Tao} and Dlugogorski, {Bogdan Z.}",
year = "2017",
month = "1",
day = "1",
doi = "10.1039/c6cy02110g",
language = "English",
volume = "7",
pages = "943--960",
journal = "Catalysis Science and Technology",
issn = "2044-4753",
publisher = "Royal Society of Chemistry (RSC)",
number = "4",

}

Jaf, ZN, Altarawneh, M, Miran, HA, Jiang, ZT & Dlugogorski, BZ 2017, 'Mechanisms governing selective hydrogenation of acetylene over γ-Mo2N surfaces', Catalysis Science and Technology, vol. 7, no. 4, pp. 943-960. https://doi.org/10.1039/c6cy02110g

Mechanisms governing selective hydrogenation of acetylene over γ-Mo2N surfaces. / Jaf, Zainab N.; Altarawneh, Mohammednoor; Miran, Hussein A.; Jiang, Zhong Tao; Dlugogorski, Bogdan Z.

In: Catalysis Science and Technology, Vol. 7, No. 4, 01.01.2017, p. 943-960.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Mechanisms governing selective hydrogenation of acetylene over γ-Mo2N surfaces

AU - Jaf, Zainab N.

AU - Altarawneh, Mohammednoor

AU - Miran, Hussein A.

AU - Jiang, Zhong Tao

AU - Dlugogorski, Bogdan Z.

PY - 2017/1/1

Y1 - 2017/1/1

N2 - Selective hydrogenation of acetylene (ethyne), present in hydrocarbon feed into ethylene (ethene) plays critical importance in processing operations. Unsupported molybdenum-nitride (Mo2N) catalysts mediate surface hydrogenation of ethyne with a profound selectivity, similar to that observed over noble metals. However, the underlying mechanisms governing the H2-C2H2-Mo2N interaction leading to partial, rather than complete, hydrogenation remain largely unclear. In this contribution, we have found that molecular hydrogen adopts several physisorbed states prior to its dissociation, mainly on 3-fold hollow fcc (H1) and 4-fold hollow fcc (H3) sites over the (111) and (100) terminations of γ-Mo2N, respectively. Our results on the interaction of hydrogen with the γ-Mo2N surface concur very well with the analogous experimental findings of the dissociation occurring preferentially on the vacant nitrogen sites, the mobility of surface-adsorbed hydrogen atoms from weak to strong adsorption sites (associated with pathways of low and high activation energies for dissociation of adsorbed H2 on the catalyst surface) and the inhibition effect of pre-adsorbed oxygen on H2 dissociation. The constructed reaction mechanism, the estimated reaction rate constants, and the micro-kinetic modelling explain the selective hydrogenation of ethyne into ethene, rather than ethane. We demonstrate that the occurrence of selective hydrogenation rests on two aspects: distinctive energy profiles of the hydrogenation steps in partial versus full hydrogenation routes and thermodynamic selectivity entailing higher surface stability of adsorbed C2H2 in comparison to C2H4. Higher stabilities of the adsorbed open-shell CxHy species (C2H3∗, C2H5∗) on the (100) surface, in comparison to those on the (111) surface, indicate increased tendency for oligomerisation to occur on the (100) surface. Thermo-kinetic parameters reported herein provide molecular-level understanding of the unique and highly selective hydrogenation capacity of the γ-Mo2N catalysts. Such knowledge is critically important in designing optimum operational conditions for practical processing operations.

AB - Selective hydrogenation of acetylene (ethyne), present in hydrocarbon feed into ethylene (ethene) plays critical importance in processing operations. Unsupported molybdenum-nitride (Mo2N) catalysts mediate surface hydrogenation of ethyne with a profound selectivity, similar to that observed over noble metals. However, the underlying mechanisms governing the H2-C2H2-Mo2N interaction leading to partial, rather than complete, hydrogenation remain largely unclear. In this contribution, we have found that molecular hydrogen adopts several physisorbed states prior to its dissociation, mainly on 3-fold hollow fcc (H1) and 4-fold hollow fcc (H3) sites over the (111) and (100) terminations of γ-Mo2N, respectively. Our results on the interaction of hydrogen with the γ-Mo2N surface concur very well with the analogous experimental findings of the dissociation occurring preferentially on the vacant nitrogen sites, the mobility of surface-adsorbed hydrogen atoms from weak to strong adsorption sites (associated with pathways of low and high activation energies for dissociation of adsorbed H2 on the catalyst surface) and the inhibition effect of pre-adsorbed oxygen on H2 dissociation. The constructed reaction mechanism, the estimated reaction rate constants, and the micro-kinetic modelling explain the selective hydrogenation of ethyne into ethene, rather than ethane. We demonstrate that the occurrence of selective hydrogenation rests on two aspects: distinctive energy profiles of the hydrogenation steps in partial versus full hydrogenation routes and thermodynamic selectivity entailing higher surface stability of adsorbed C2H2 in comparison to C2H4. Higher stabilities of the adsorbed open-shell CxHy species (C2H3∗, C2H5∗) on the (100) surface, in comparison to those on the (111) surface, indicate increased tendency for oligomerisation to occur on the (100) surface. Thermo-kinetic parameters reported herein provide molecular-level understanding of the unique and highly selective hydrogenation capacity of the γ-Mo2N catalysts. Such knowledge is critically important in designing optimum operational conditions for practical processing operations.

UR - http://www.scopus.com/inward/record.url?scp=85014718273&partnerID=8YFLogxK

U2 - 10.1039/c6cy02110g

DO - 10.1039/c6cy02110g

M3 - Article

VL - 7

SP - 943

EP - 960

JO - Catalysis Science and Technology

JF - Catalysis Science and Technology

SN - 2044-4753

IS - 4

ER -