The bi-functional mechanism of CH4 dry reforming over a Ni–CaO–ZrO2 catalyst: further evidence via the identification of the active sites and kinetic studies

The dry reforming of methane is a promising technology for the abatement of CH4 and CO2. Solid solution Ni–La oxide catalysts are characterized by their long–term stability (100h) when tested at full conversion. The kinetics of dry reforming over this type of catalysts has been studied using both power law and Langmuir–Hinshelwood based approaches. However, these studies typically deal with fitting the net CH4 rate hence disregarding competing and parallel surface processes and the different possible configurations of the active surface. In this work, we synthesized a solid solution Ni–La oxide catalyst and tested six Langmuir–Hinshelwood mechanisms considering both single and dual active sites for assessing the kinetics of dry reforming and the competing reverse water gas shift reaction and investigated the performance of the derived kinetic models. In doing this, it was found that: (1) all the net rates were better fitted by a single–site model that considered that the first C–H bond cleavage in methane occurred over a <a>metal−oxygen </a>pair site; (2) this model predicted the existence of a nearly saturated nickel surface with chemisorbed oxygen adatoms derived from the dissociation of CO2; (3) the dissociation of CO2 can either be an inhibitory or an irrelevant step, and it can also modify the apparent activation energy for CH4 activation. These findings contribute to a better understanding of the dry reforming reaction's kinetics and provide a robust kinetic model for the design and scale–up of the process.

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Atomically dispersed nickel as coke-resistant active sites for methane dry reforming

Nature Communications ◽

10.1038/s41467-019-12843-w ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 46

Author(s):

Mohcin Akri ◽

Shu Zhao ◽

Xiaoyu Li ◽

Ketao Zang ◽

Adam F. Lee ◽

...

Keyword(s):

Active Sites ◽

Large Scale ◽

Low Cost ◽

Coke Formation ◽

Dry Reforming ◽

Dry Reforming Of Methane ◽

Highly Active ◽

Catalytic Sites ◽

Earth Abundant ◽

Poor Stability

AbstractDry reforming of methane (DRM) is an attractive route to utilize CO2 as a chemical feedstock with which to convert CH4 into valuable syngas and simultaneously mitigate both greenhouse gases. Ni-based DRM catalysts are promising due to their high activity and low cost, but suffer from poor stability due to coke formation which has hindered their commercialization. Herein, we report that atomically dispersed Ni single atoms, stabilized by interaction with Ce-doped hydroxyapatite, are highly active and coke-resistant catalytic sites for DRM. Experimental and computational studies reveal that isolated Ni atoms are intrinsically coke-resistant due to their unique ability to only activate the first C-H bond in CH4, thus avoiding methane deep decomposition into carbon. This discovery offers new opportunities to develop large-scale DRM processes using earth abundant catalysts.

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Ultrathin Washcoat and Very Low Loading Monolithic Catalyst with Outstanding Activity and Stability in Dry Reforming of Methane

Nanomaterials ◽

10.3390/nano10030445 ◽

2020 ◽

Vol 10 (3) ◽

pp. 445 ◽

Cited By ~ 1

Author(s):

Fazia Agueniou ◽

Hilario Vidal ◽

María Pilar Yeste ◽

Juan C. Hernández-Garrido ◽

Miguel A. Cauqui ◽

...

Keyword(s):

Thermodynamic Limit ◽

Catalyst Layer ◽

Active Phase ◽

Dry Reforming ◽

Redox Properties ◽

Dry Reforming Of Methane ◽

Alumina Catalyst ◽

Monolithic Catalyst ◽

Prolonged Time ◽

Zro2 Catalyst

A Ni/CeO2/ZrO2 catalyst with improved redox properties has been washcoated onto a honeycomb cordierite monolith in the form of a nonconventional alumina-catalyst layer, just a few nanometers thick. In spite of the very low active phase loading, the monolith depicts outstanding performance in dry reforming of methane, both in terms of activity, with values reaching the thermodynamic limit already at 750 °C, even under extreme Weight Hourly Space Velocities (WHSV 115–346 L·g−1·h−1), as well as in terms of stability during prolonged Time on Stream (TOS 24–48 h).

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Low-Temperature Catalytic CO2 Dry Reforming of Methane on Ni-Si/ZrO2 Catalyst

ACS Catalysis ◽

10.1021/acscatal.8b00584 ◽

2018 ◽

Vol 8 (7) ◽

pp. 6495-6506 ◽

Cited By ~ 55

Author(s):

Ye Wang ◽

Lu Yao ◽

Yannan Wang ◽

Shenghong Wang ◽

Qing Zhao ◽

...

Keyword(s):

Low Temperature ◽

Dry Reforming ◽

Dry Reforming Of Methane ◽

Zro2 Catalyst

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Evaluation of a Catalyst Durability in Absence and Presence of Toluene Impurity: Case of the Material Co2Ni2Mg2Al2 Mixed Oxide Prepared by Hydrotalcite Route in Methane Dry Reforming to Produce Energy

Materials ◽

10.3390/ma12091362 ◽

2019 ◽

Vol 12 (9) ◽

pp. 1362

Author(s):

Carole Tanios ◽

Cédric Gennequin ◽

Madona Labaki ◽

Haingomalala Lucette Tidahy ◽

Antoine Aboukaïs ◽

...

Keyword(s):

Catalytic Activity ◽

Mixed Oxide ◽

Active Sites ◽

Dry Reforming ◽

Dry Reforming Of Methane ◽

Side Reactions ◽

Commercial Catalyst ◽

Catalytic Sites ◽

Catalyst Durability ◽

Catalytic Performances

Ni, Co, Mg, and Al mixed-oxide solids, synthesized via the hydrotalcite route, were investigated in previous works toward the dry reforming of methane for hydrogen production. The oxide Co2Ni2Mg2Al2 calcined at 800 °C, Co2Ni2Mg2Al2800, showed the highest catalytic activity in the studied series, which was ascribable to an interaction between Ni and Co, which is optimal for this Co/Ni ratio. In the present study, Co2Ni2Mg2Al2800 was compared to a commercial catalyst widely used in the industry, Ni(50%)/Al2O3, and showed better activity despite its lower number of active sites, as well as lower amounts of carbon on its surface, i.e. less deactivation. In addition to this, Co2Ni2Mg2Al2800 showed stability for 20 h under stream during the dry reforming of methane. This good durability is attributed to a periodic cycle of carbon deposition and removal as well as to the strong interaction between Ni and Co, preventing the deactivation of the catalyst. The evaluation of the catalytic performances in the presence of toluene, which is an impurity that exists in biogas, is also a part of this work. In the presence of toluene, the catalytic activity of Co2Ni2Mg2Al2800 decreases, and higher carbon formation on the catalyst surface is detected. Toluene adsorption on catalytic sites, side reactions performed by toluene, and the competition between toluene and methane in the reaction with carbon dioxide are the main reasons for such results.

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Hydroxylation of C–H bonds at carboxylate-bridged diiron centres

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2004.1532 ◽

2005 ◽

Vol 363 (1829) ◽

pp. 861-877 ◽

Cited By ~ 53

Author(s):

Stephen J Lippard

Keyword(s):

Active Sites ◽

Bond Activation ◽

Kinetic Studies ◽

Methyl Radical ◽

Α Subunit ◽

Model Complexes ◽

Soluble Methane Monooxygenase ◽

Related Enzyme ◽

High Valent ◽

Rate Limiting

Nature uses carboxylate-bridged diiron centres at the active sites of enzymes that catalyse the selective hydroxylation of hydrocarbons to alcohols. The resting diiron(III) state of the hydroxylase component of soluble methane monooxygenase enzyme is converted by two-electron transfer from an NADH-requiring reductase into the active diiron(II) form, which subsequently reacts with O 2 to generate a high-valent diiron(IV) oxo species (Q) that converts CH 4 into CH 3 OH. In this step, C–H bond activation is achieved through a transition state having a linear C⋯H⋯O unit involving a bound methyl radical. Kinetic studies of the reaction of Q with substrates CH 3 X, where X=H, D, CH 3 , NO 2 , CN or OH, reveal two classes of reactivity depending upon whether binding to the enzyme or C–H bond activation is rate-limiting. Access of substrates to the carboxylate-bridged diiron active site in the hydroxylase (MMOH) occurs through a series of hydrophobic pockets. In the hydroxylase component of the closely related enzyme toluene/ o -xylene monooxygenase (ToMOH), substrates enter through a wide channel in the α-subunit of the protein that tracks a course identical to that found in the structurally homologous MMOH. Synthetic models for the carboxylate-bridged diiron centres in MMOH and ToMOH have been prepared that reproduce the stoichiometry and key geometric and physical properties of the reduced and oxidized forms of the proteins. Reactions of the diiron(II) model complexes with dioxygen similarly generate reactive intermediates, including high-valent species capable not only of hydroxylating pendant C–H bonds but also of oxidizing phosphine and sulphide groups.

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Rate-determining processes and the number of simultaneously active sites of d-glyceraldehyde 3-phosphate dehydrogenase

Biochemical Journal ◽

10.1042/bj1220071 ◽

1971 ◽

Vol 122 (1) ◽

pp. 71-77 ◽

Cited By ~ 42

Author(s):

D. R. Trentham

Keyword(s):

Oxidative Phosphorylation ◽

Active Sites ◽

Dissociation Constants ◽

Kinetic Studies ◽

Competitive Inhibitor ◽

Low Ph ◽

Conformation Change ◽

High Ph ◽

Rate Determining Step ◽

Transient Experiments

Transient kinetic studies of the reversible oxidative phosphorylation of d-glyceraldehyde 3-phosphate catalysed by d-glyceraldehyde 3-phosphate dehydrogenase show that all four sites of the tetrameric lobster enzyme are simultaneously active, apparently with equal reactivity. The rate-determining step of the oxidative phosphorylation is NADH release at high pH and phosphorolysis of the acyl-enzyme at low pH. For the reverse reaction the rate-determining step is a process associated with NADH binding, probably a conformation change, at high pH and d-glyceraldehyde 3-phosphate release at low pH. NADH has previously been shown to be a competitive inhibitor of the enzyme with respect to d-glyceraldehyde 3-phosphate and vice versa. This is consistent with the mechanism deduced from transient experiments given the additional proviso that 1-arseno-3-phosphoglycerate has a half-life of about 1min or longer at pH7. The dissociation constants of d-glyceraldehyde 3-phosphate and 1,3-diphosphoglycerate to the NAD+-bound enzyme are too large to measure but are nevertheless consistent with the low Km values of these substrates.

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Nanostructured faujasite zeolite as metal ion adsorbent: kinetics, equilibrium adsorption and metal recovery studies

Water Science & Technology ◽

10.2166/wst.2020.580 ◽

2020 ◽

Author(s):

Mariana B. Goncalves ◽

Djanyna V. C. Schmidt ◽

Fabiana S. dos Santos ◽

Daniel F. Cipriano ◽

Gustavo R. Gonçalves ◽

...

Keyword(s):

Ion Exchange ◽

Metal Ions ◽

Metal Ion ◽

Active Sites ◽

Metal Removal ◽

High Surface ◽

High Surface Area ◽

Kinetic Studies ◽

Crystallization Time ◽

X Ray

Abstract The hydrothermal synthesis of nano-faujasite has been successfully performed and the effects of some crystallization parameters were investigated, along with the use of this material as a heavy-metal ion adsorbent. X-ray diffraction patterns have shown that the structure of the nano-faujasite is strongly dependent on both the crystallization time and the alkalinity of the synthesis medium. According to N2 physisorption, X-ray fluorescence, SEM/EDS, and solid state 29Si and 27Al NMR data, the produced nano-faujasite consists of a solid with low molar Si/Al ratio (1.7), with high availability of ion exchange sites and high surface area/small particle size, allowing easy diffusion of metal ions to adsorbent active sites. As a consequence, an excellent performance on removal of Cd2+, Zn2+ and Cu2+ ions was found for this solid. The adsorption capacity followed the order Cd2+ (133 mg·g−1) > Zn2+ (115 mg·g−1) > Cu2+ (99 mg·g−1), which agrees with the order of increasing absolute values of the hydration energy of the metal ions. Kinetic studies and adsorption isotherms showed that the metal ion removal takes place by ion exchange on the monolayer surface of the nano-faujasite. The electrochemical recovery of copper in metallic form exhibited an efficiency of 80.2% after 120 min, which suggests that this process can be adequately implemented for full-scale metal removal.

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