Journal Article

# Optimizing Active Sites for High CO Selectivity during CO2 Hydrogenation over Supported Nickel Catalysts

04 Mar 2021-Journal of the American Chemical Society (American Chemical Society)-Vol. 143, Iss: 11, pp 4268-4280
Abstract: Controlling the selectivity of CO2 hydrogenation catalysts is a fundamental challenge. In this study, the selectivity of supported Ni catalysts prepared by the traditional impregnation method was f...

Topics: Selectivity (52%), Catalysis (52%)
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Open accessJournal Article
Md. Imteyaz Alam1, Raffaele Cheula1, Gianluca Moroni1, Luca Nardi1  +1 moreInstitutions (1)
Abstract: The increasing environmental concerns due to anthropogenic CO2 emissions have called for an alternate sustainable source to fulfill rising chemical and energy demands and reduce environmental problems. The thermo-catalytic activation and conversion of abundantly available CO2, a thermodynamically stable and kinetically inert molecule, can significantly pave the way to sustainably produce chemicals and fuels and mitigate the additional CO2 load. This can be done through comprehensive knowledge and understanding of catalyst behavior, reaction kinetics, and reactor design. This review aims to catalog and summarize the advances in the experimental and theoretical approaches for CO2 activation and conversion to C1 products via heterogeneous catalytic routes. To this aim, we analyze the current literature works describing experimental analyses (e.g., catalyst characterization and kinetics measurement) as well as computational studies (e.g., microkinetic modeling and first-principles calculations). The catalytic reactions of CO2 activation and conversion reviewed in detail are: (i) reverse water-gas shift (RWGS), (ii) CO2 methanation, (iii) CO2 hydrogenation to methanol, and (iv) dry reforming of methane (DRM). This review is divided into six sections. The first section provides an overview of the energy and environmental problems of our society, in which promising strategies and possible pathways to utilize anthropogenic CO2 are highlighted. In the second section, the discussion follows with the description of materials and mechanisms of the available thermo-catalytic processes for CO2 utilization. In the third section, the process of catalyst deactivation by coking is presented, and possible solutions to the problem are recommended based on experimental and theoretical literature works. In the fourth section, kinetic models are reviewed. In the fifth section, reaction technologies associated with the conversion of CO2 are described, and, finally, in the sixth section, concluding remarks and future directions are provided.

2 Citations

Journal Article
Tiancheng Pu1, Tiancheng Pu2, Liang Shen2, Xianglin Liu2  +4 moreInstitutions (2)
Abstract: Hydroxyl formation on metallic Ni sites and Ni-SiO2 interfacial region of Ni/SiO2 during CO2 hydrogenation is characterized for the first time with the aid of H2-TPR, CO-TPR, quasi in situ XPS and in situ DRIFTS of adsorbed CO. These reaction-generated hydroxyl groups are distinct from those existing on SiO2 surfaces and can decrease the binding strength of CO, hampering its further hydrogenation, particularly for smaller nickel nanoparticles, as evidence by the DFT calculations. This fact contributes to the product selectivity of CO2 hydrogenation over nickel nanoparticles with different sizes. The experimental and theoretical observations shed lights on the characterization of surface hydroxyls and rational design of heterogeneous catalysis through fine tuning of surface reaction intermediates by optimization of particle size.

Topics: Catalysis (54%), Nickel (52%),

2 Citations

Journal Article
Feiyang Hu1, Xiaohan Chen1, Ziao Tu1, Zhang-Hui Lu2  +2 moreInstitutions (2)
Topics: Graphene (56%), Aerogel (53%), Methane (51%)

1 Citations

Journal Article
Ruoyu Zhang1, Anlu Wei1, Min Zhu1, Xiaoxia Wu1  +3 moreInstitutions (2)
Abstract: Catalytic reduction of CO2 to CO via reverse water gas shift (RWGS) reaction provides a feasible approach to utilize CO2, since CO can be further converted to various versatile products through the syngas routes. Ni-based catalysts are low cost and have a high activity for CO2 reduction but are nonselective for RWGS due to competition from methanation. In this work, we demonstrated that surface modification of Ni by MoOx can be tailored to tune the reactions of RWGS and methanation. The addition of MoOx improves Ni dispersion through strong interactions whereas partially reduced MoOx modifies the surface of Ni particles through both geometric coverage and electronic modification. No CO adsorption was observed at room temperature on the NiMo catalyst with a Mo/Ni ratio of 1, confirmed by density functional theory calculation. Tracking product evolution showed that CO2 is first reduced to CO through RWGS on the Ni catalysts and methane is a product of CO hydrogenation. Apparent activation energy analysis indicates that the overall reaction is controlled by CO desorption. Addition of a small amount of Mo (Mo/Ni ratio of 0.1) shifts the reaction further to methanation selective with ∼100% CH4 selectivity as MoOx aids in the activation of both CO2 and CO. In contrast, the addition of a large amount of Mo (Mo/Ni ratio of 1) shifts the reaction to RWGS selective with a CO selectivity > 94%. This is attributed to the enhanced CO desorption from the surface as a result of MoOx modification.

Topics: Methanation (59%), Catalysis (50%),  ... read more

1 Citations

Open accessPosted Content
Bjarne Kreitz1, Bjarne Kreitz2, Khachik Sargsyan3, Katrin Blondal1  +5 moreInstitutions (4)
16 Aug 2021-ChemRxiv
Abstract: Automatic mechanism generation is used to determine mechanisms for the CO2 hydrogenation on Ni(111) in a two-stage process while considering the correlated uncertainty in DFT-based energetic parameters systematically. In a coarse stage, all the possible chemistry is explored with gas-phase products down to the ppb level, while a refined stage discovers the core methanation submechanism. Five thousand unique mechanisms were generated, which contain minor perturbations in all parameters. Global uncertainty assessment, global sensitivity analysis, and degree of rate control analysis are performed to study the effect of this parametric uncertainty on the microkinetic model predictions. Comparison of the model predictions with experimental data on a Ni/SiO2 catalyst find a feasible set of microkinetic mechanisms within the correlated uncertainty space that are in quantitative agreement with the measured data, without relying on explicit parameter optimization. Global uncertainty and sensitivity analyses provide tools to determine the pathways and key factors that control the methanation activity within the parameter space. Together, these methods reveal that the degree of rate control approach can be misleading if parametric uncertainty is not considered. The procedure of considering uncertainties in the automated mechanism generation is not unique to CO2 methanation and can be easily extended to other challenging heterogeneously catalyzed reactions.

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Peter E. Blöchl1Institutions (1)
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Georg Kresse1, Daniel P. Joubert2Institutions (2)
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Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.

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Georg Kresse1, Jürgen Furthmüller2Institutions (2)
Abstract: We present a detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set. We will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temperature density-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order Natoms2 scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge density including a new special ‘preconditioning’ optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. We have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio molecular-dynamics package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.