Dissociation of methane on Ni 4 cluster-A DFT study

Roy, Ghanashyam; Chattopadhyay, Asoke P.

doi:10.1016/j.comptc.2017.02.030

Cited by 25 publications

(21 citation statements)

References 32 publications

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“…The elementary step 1 is thermodynamically favorable(ΔG, −0.22 eV ) at standard condition (T=298 K, P=1 atm), and the calculated activation energy barrier is 0.72 eV. Whereas on pure Ni 4 cluster, the calculated activation barrier for the step is 1.28 eV, and thermodynamically not favorable at normal condition. Burghgraef et al .…”

Section: Resultsmentioning

confidence: 91%

“…Smaller the size of the particle, larger the number surface atoms take part in the reaction. Thus, the dissociation of methane is performed on the clusters of size as small as Ni 4 , Ni 7 , and Ni 13 , etc. Particle size dependant coke inhibition is also observed experimentally applying Ni nanoparticles .…”

Section: Introductionmentioning

confidence: 99%

“…However, small size particle does not show better performance always . Recently, Chattopadhyay et al . calculated the coke formation temperature is above 525 K at 1 atm on tetrahedral Ni 4 cluster.…”

Section: Introductionmentioning

confidence: 99%

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Methane Dissociation on Bimetallic AuNi₃, Au₂Ni₂ and Au₃Ni Clusters‐A DFT Study

Roy

Chattopadhyay

2018

ChemistrySelect

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The effect of gold atom for the dissociation of methane on tetrahedral bimetallic Au x Ni y (x + y = 4; x,y = 1-3) clusters are introduced using density functional theory method. The binding energy and HOMO-LUMO gap fluctuate with odd-even number of gold atoms. The clusters, AuNi 3 and Au 3 Ni, containing odd number of doped gold atoms, which causes open shell configuration, are exceptionally stable and highly resistance to carbon deposition, whereas closed shell Au 2 Ni 2 cluster is less stable. As the number of doped Au atom increases in the clusters, adsorption or binding energy of methane increases. The dissociation of methane is a four elementary steps process, and first step of dissociation, CH 4 ! CH 3 , is not the rate determining step, and thermodynamically favorable at room temperature and pressure for the clusters due to adsorption. Whereas, the dissociation of CH!C, coke formation step 4, is the rate determining step due to highest energy barrier for all the clusters. The calculated activation energies for the rate determining step are 0.92 eV, 0.41 eV and 1.64 eV for AuNi 3 , Au 2 Ni 2 and Au 3 Ni clusters, respectively. In addition, the dissociation temperature for all the intermediates, e. g., CH 3 , CH 2 and CH are 450 K(CH 3 and CH 2 ) and 650 K(CH) on AuNi 3 cluster; 450 K(CH 3 ) and 550 K(CH 2 and CH) on Au 2 Ni 2 cluster; and 650 K(CH 3 ), 750 K(CH 2 ) and 950 K(CH) on Au 3 Ni cluster. Thus, the coke resistivity decreases as Au 3 Ni > AuNi 3 > Au 2 Ni 2 and corresponding coke resistance temperatures are 950 K, 650 K and 550 K, respectively. The charge tranfer to the clusters during adsorption is negative, and is positive in the dissociation steps. Thus, the number of doped gold atom not only influences the stability of bimetallic AuÀNi clusters, but also their reactivity towards methane, which can provide some new insight for the design of coke resistant catalysts for methane reforming.[a] Prof.

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Section: Resultsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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Methane Dissociation on Bimetallic AuNi₃, Au₂Ni₂ and Au₃Ni Clusters‐A DFT Study

Roy

Chattopadhyay

2018

ChemistrySelect

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“…The three-dimensional tetrahedral Ni 4 cluster is used as a model to understand the reactivity of hydrazine at molecular level on surface of Ni catalyst particle. The optimised geometrical parameters of Ni 4 cluster is presented in our earlier papers [56,57]. However, to obtain stable configuration of adsorption, different possible adsorption configurations were optimised by placing the conformers of hydrazine on the binding sites of Ni 4 cluster, as shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…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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