Mechanism of CO methanation on the Ni4/γ-Al2O3 and Ni3Fe/γ-Al2O3 catalysts: A density functional theory study

Wang, Yanxin; Su, Yan; Kang, Lihua

doi:10.1016/j.ijhydene.2015.05.002

Cited by 36 publications

(16 citation statements)

References 54 publications

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“…Based on the above-mentioned results, the optimal pathway of CH 4 the rate-determining step is the direct dissociation of CH 3 O species, which is consistent with those on the Ni 4 /g-Al 2 O 3 15 and Ni 4 /SiC catalyst surfaces. 25 Figure 8 shows the potential energy profile for syngas methanation on the Ni 4 /MCM-41 catalyst surface.…”

Section: Discussionsupporting

confidence: 76%

Study on syngas methanation mechanism over Ni₄/MCM-41 catalyst based on density functional theory

Zhang

2019

Progress in Reaction Kinetics and Mechanism

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The density functional theory method is employed to systematically explore the mechanism of syngas methanation on the Ni4/MCM-41 catalyst surface. The calculation results show that the optimal pathway of CH4 formation is CO + H → CHO + H → CH2O + H → CH3O → CH3 + H → CH4 with the rate-determining step of CH3O direct dissociation. Because the activation energy for the direct dissociation of CH3O species is much lower than that for the CH3OH formation (198.6 vs 264.8 kJ mol−1), there is almost no by-product CH3OH that appeared in the products of the syngas methanation over the Ni4/MCM-41 catalyst. Compared with other conventional nickel-based methanation catalysts, Ni4/MCM-41 catalyst is an excellent methanation catalyst with high selectivity of CH4.

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Section: Discussionsupporting

confidence: 76%

Study on syngas methanation mechanism over Ni₄/MCM-41 catalyst based on density functional theory

Zhang

2019

Progress in Reaction Kinetics and Mechanism

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“…CO $ CH 4 ? H 2 O) (Shinde and Madras 2014;Wang et al 2015). The CO methanation reaction is a key process for increasing SNG production (Meng et al 2015b;Götz et al 2016;Gao et al 2016).…”

Section: List Of Symbolsmentioning

confidence: 99%

CO hydrogenation combined with water-gas-shift reaction for synthetic natural gas production: a thermodynamic and experimental study

Meng

et al. 2017

Int J Coal Sci Technol

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The hydrogenation of CO to synthetic natural gas (SNG) needs a high molar ratio of H 2 /CO (usually large than 3.0 in industry), which consumes a large abundant of hydrogen. The reverse dry reforming reaction (RDR, 2H 2 ? 2CO $ CH 4 ? CO 2 ), combining CO methanation with water-gas-shift reaction, can significantly decrease the H 2 /CO molar ratio to 1 for SNG production. A detailed thermodynamic analysis of RDR reaction was carried out based on the Gibbs free energy minimization method. The effect of temperature, pressure, H 2 /CO ratio and the addition of H 2 O, CH 4 , CO 2 , O 2 and C 2 H 4 into the feed gas on CO conversion, CH 4 and CO 2 selectivity, as well as CH 4 and carbon yield, are discussed. Experimental results obtained on homemade impregnated Ni/Al 2 O 3 catalyst are compared with the calculations. The results demonstrate that low temperature (200-500°C), high pressure (1-5 MPa) and high H 2 /CO ratio (at least 1) promote CO conversion and CH 4 selectivity and decrease carbon yield. Steam and CO 2 in the feed gas decrease the CH 4 selectivity and carbon yield, and enhance the CO 2 content. Extra CH 4 elevates the CH 4 content in the products, but leads to more carbon formation at high temperatures. O 2 significantly decreases the CH 4 selectivity and C 2 H 4 results in the generation of carbon.Keywords Synthetic natural gas Á Reverse dry reforming of methane Á Gibbs free energy minimization Á Experimental study Á CO conversion List of symbols A k Total mass of k element in the feed f i H Standard-state fugacity of species i (Pa) f i

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“…as a model of Shell 405 catalyst. However, several small Ni 4 cluster-based calculations are also reported to clarify the decomposition of small molecules on such surfaces [55][56][57]. To our knowledge, the dissociation of hydrazine on Ni 4 cluster has not been reported till date.…”

Section: Introductionmentioning

confidence: 99%

Dissociation of hydrazine on tetrahedral Ni4 cluster by density functional theory

Roy¹,

Chattopadhyay

2019

SN Appl. Sci.

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Sequential dissociation of hydrazine has been studied on Ni 4 cluster applying density functional theory (DFT) methods. Two routes of dissociation have been discussed. The first path (A) is the consecutive dissociation of four N-H bonds to form surface N 2 via intermediate product diimide, N 2 H 2. The second path (B) is the dissociation of N-N bond to form two NH 2 species leading to formation of surface ammonia. The second elementary steps for both the routes show the highest activation energy barrier; for example in path A, N 2 H 3 + H → N 2 H 2 + 2H, E Act is 1.19 eV and in path B, 2NH 2 → NH + H+NH 2 , E Act is 1.71 eV. These are the rate-determining steps. NBO analysis shows that adsorption of hydrazine and ammonia is due to strong delocalisation of the lone pairs to the higher energy states of the cluster. Adsorption and dissociation of hydrazine and ammonia are thermodynamically feasible at standard conditions. Formation of N 2 is a slow exothermic process, whereas N-N bond dissociation to form two NH 2 species is a faster and highly exothermic process. NH species binds by two Ni-N covalent bonds. N species binds the cluster by three Ni-N bonds and three strong lone pair delocalisation at threefold site. Removal of these intermediates needs higher energy of activation. Thus, the formation and dehydrogenation of ammonia are slow and lengthy processes. New catalysts could be designed in such a way that N-N bond might not be dissociated, which is happening due to absence of lone pair of N1(LP) to Rydberg orbital of N2(RY*) delocalisation or vice versa.

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Mechanism of CO methanation on the Ni4/γ-Al2O3 and Ni3Fe/γ-Al2O3 catalysts: A density functional theory study

Cited by 36 publications

References 54 publications

Study on syngas methanation mechanism over Ni₄/MCM-41 catalyst based on density functional theory

Study on syngas methanation mechanism over Ni₄/MCM-41 catalyst based on density functional theory

CO hydrogenation combined with water-gas-shift reaction for synthetic natural gas production: a thermodynamic and experimental study

Dissociation of hydrazine on tetrahedral Ni4 cluster by density functional theory

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Mechanism of CO methanation on the Ni4/γ-Al2O3 and Ni3Fe/γ-Al2O3 catalysts: A density functional theory study

Cited by 36 publications

References 54 publications

Study on syngas methanation mechanism over Ni4/MCM-41 catalyst based on density functional theory

Study on syngas methanation mechanism over Ni4/MCM-41 catalyst based on density functional theory

CO hydrogenation combined with water-gas-shift reaction for synthetic natural gas production: a thermodynamic and experimental study

Dissociation of hydrazine on tetrahedral Ni4 cluster by density functional theory

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Study on syngas methanation mechanism over Ni₄/MCM-41 catalyst based on density functional theory

Study on syngas methanation mechanism over Ni₄/MCM-41 catalyst based on density functional theory