Nucleation and Initial Stages of Growth during the Atomic Layer Deposition of Titanium Oxide on Mesoporous Silica

Wang, Ke; Liu, Yang; Wang, Xuelong; Qin, Xiangdong; Chen, Limei; Palomino, Robert M.; Simonovis, Juan Pablo; Lee, Ilkeun; Waluyo, Iradwikanari; Rodríguez, José A.; Frenkel, Anatoly I.; Liu, Ping; Zaera, Francisco

doi:10.1021/acs.nanolett.0c02990

Cited by 28 publications

(41 citation statements)

References 42 publications

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“…On the contrary, no distinguishable peak of the 2–3 nm distribution and the low intensity of the mesopore distribution were explored for the TiO 2 /C structure catalyst and further decreased after Pt had been decorated on the TiO 2 /C. This behavior is expected because the mesopores became smaller and closed via continuous thin films or dense particles on the carbon surface . To determine the Ti chemical state, the O 1s peak of the XPS spectra was scanned for Pt/TiO 2 /C and TiO 2 /Pt/C catalysts.…”

Section: Resultsmentioning

confidence: 99%

“…This behavior is expected because the mesopores became smaller and closed via continuous thin films or dense particles on the carbon surface. 37 To determine the Ti chemical state, the O 1s peak of the XPS spectra was scanned for Pt/TiO 2 /C and TiO 2 /Pt/C catalysts. As shown in Figure 2d, O bonded with carbon as well as others in the Pt/TiO 2 /C catalyst was dominant; the TiO 2 /Pt/C catalyst displayed a strong Ti−O state, and a Pt−O bonding peak was observed.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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In Situ Engineering of a Metal Oxide Protective Layer into Pt/Carbon Fuel-Cell Catalysts by Atomic Layer Deposition

et al. 2022

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Degradation of polymer electrolyte membrane fuel cell (PEMFC) systems has emerged as a critical issue. A thin metal oxide layer coated with Pt/carbon via ALD (atomic layer deposition) is one of the potential approaches for preserving electrochemical activity; however, the exact interfacial effects of metal oxide on enhancing PEMFC durability are unclear. Herein, interfacial engineering of the TiO 2 layers within the in situ-synthesized Pt/carbon catalysts (Pt/TiO 2 /C and TiO 2 /Pt/C) was studied using fluidized bed reactor (FBR) ALD to investigate the exact effects of the catalysts. For the Pt/TiO 2 /C catalyst, the TiO 2 layer was first conformally coated on the carbon surfaces, whereas for TiO 2 /Pt/C, the TiO 2 layer was selectively formed on the Pt NP surface via the ALD mechanism. The Pt/TiO 2 /C catalyst has a higher Pt loading with suppressed micropores due to the introduction of the TiO 2 layer on the carbon support, whereas the TiO 2 /Pt/C catalyst remained in the 2−3 nm mesopores. The electrochemical durability of both ALD catalysts is superior to that of the commercial Pt catalyst. Encapsulating the TiO 2 layer on the Pt surface specializing in blocking Pt dissolution resulted in better long-term stability of the electrochemical characteristics compared to the stability of those of Pt/TiO 2 / C, which especially showed the better initial performance of the electrochemically active surface area, oxygen reduction reaction, and PEMFC single-cell performance. This study provides the direction and steps toward an efficient nanostructure design of metal oxide by ALD in most catalyst fields.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

In Situ Engineering of a Metal Oxide Protective Layer into Pt/Carbon Fuel-Cell Catalysts by Atomic Layer Deposition

et al. 2022

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“…tory. 2210,2217,2255,2257 In one example, mixed −Al−O−Si− oxide sites with Brønsted-acid properties were created by adding submonolayer coverages of silica to Pt/Al 2 O 3 catalysts, as identified by IR titration experiments using pyridine as the probe molecule (Figure 163, left panel). 2257 These new sites proved to help increase selectivity during the hydrogenation of unsaturated aldehydes (cinnamaldehyde, CMA) toward the desired unsaturated alcohol product (cinnamyl alcohol, CMO), as shown in the right panel of Figure 163.…”

Section: Atomic Layer Depositionmentioning

confidence: 99%

“…New redox sites can also be made via the ALD of reducible oxide films such as titania or ceria. 2255 The fact that it is the mixedoxide interface the responsible for the new chemistry is suggested by the fact that in many cases optimum selectivity is seen at coverages of approximately half a monolayer of the new oxide film. 2217,2255,2257 With metals, the deposition of smooth and uniform films is difficult, and, because of their low surface tension, those are unstable toward sintering and NP formation.…”

Section: Atomic Layer Depositionmentioning

confidence: 99%

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

Zaera

2022

Chem. Rev.

Self Cite

207

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A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

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“…Foi relatado na literatura que o número inicial de sítios de nucleação (grupos Si-OH de superfície) na SBA-15 é de 1,8 mmol.g -1 . (IDE et al, 2013;KE et al, 2020) Com base nisso, os dados na Figura 68 e na Tabela 22 indicam que, neste caso, deve levar cerca de 3 ciclos de ZrO2 ALD para reagir a todos esses locais de nucleação para criar a primeira monocamada. NGSBAZr_6, feito com 6 ciclos de ALD de ZrO2, nota-se a presença de poros com 3,6, 4,2 e 5,1 nm, indicando que neste material houve a deposição de ZrO2 mais efetiva, já que houve a diminuição do diâmetro de poros, porém a deposição não foi homogênea, já que surgiram poros com 4,2 e 5,1 nm.…”

Section: Methodsunclassified

Estudo de catalisadores do tipo Ni-Ga para a síntese de metanol a partir da hidrogenação do CO>sub<2>/sub< em baixas pressões

Rasteiro¹

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Given the industrial development and large population growth in the last years, the uncontrolled emission of greenhouse gases, especially CO2, has generated great concern for the environment and life on Earth. Thereby, policies for containment and CO2 utilization began to be widely studied, as in the case of some reactions where CO2 is converted into value-added products. Among several options for its use, the hydrogenation of CO2 to produce methanol has drawn a lot of attention because methanol is an important raw material for the industry and has a growing demand in the world market. Cu-based catalysts are the most used catalyst in this reaction, but more recently the discovery of Ni-Ga type catalysts with good activity at low pressures has grabbed the attention of the scientific community. Despite being promising, little has been studied about these catalysts and how they act in the reaction. In this context, this work aims to study supported and unsupported Ni-Ga alloy catalysts in methanol synthesis through CO2 hydrogenation at low pressures. The first part of this work seeks to understand the behavior of the unsupported Ni5Ga3 alloy, for example, which physicochemical characteristics of the alloy exert the biggest influence on the reaction, and which intermediates and reaction mechanisms take place on it. In this step, it was noticed that the particle size exerts a strong influence on the catalytic activity and that the reaction takes place through two reaction routes on the alloy, rWGS, and formate. The second part of the work explored the Ni5Ga3 alloy supported on basic oxides, in order to improve the catalytic activity, since the conversions and selectivity were low in the unsupported alloy. The use of supports improved the catalytic activity and the alloy supported on ZrO2 showed the best result, and it was concluded that it is due to the interaction strengths of the reaction intermediates and reagents with the Ni5Ga3-ZrO2 interface. In the third step, the behavior of the alloy on mesoporous inert supports with high surface area (MCM-41 and SBA-15) was studied. It was observed through in situ analysis techniques that the decrease in the density of metallic sites disfavored the adsorption of CO on the surface and, therefore, lower selectivity and conversion to methanol was obtained compared to the reference sample. The fourth and last part of the work united the best basic support used in the second part with the best among the high-area mesoporous supports used in the third part, preparing new catalysts through the ALD technique of ZrO2 on pure SBA-15 or an already impregnated SBA-15 with Ni5Ga3. Among the two groups of prepared materials, it was noted that more ALD cycles were favorable to produce methanol intermediates and that the impregnation of Ni5Ga3 after ALD of ZrO2 on SBA-15 led the reaction to follow only the formate route, different from what happened with the other group, being very desirable for a high selectivity for methanol.

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Nucleation and Initial Stages of Growth during the Atomic Layer Deposition of Titanium Oxide on Mesoporous Silica

Cited by 28 publications

References 42 publications

In Situ Engineering of a Metal Oxide Protective Layer into Pt/Carbon Fuel-Cell Catalysts by Atomic Layer Deposition

In Situ Engineering of a Metal Oxide Protective Layer into Pt/Carbon Fuel-Cell Catalysts by Atomic Layer Deposition

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

Estudo de catalisadores do tipo Ni-Ga para a síntese de metanol a partir da hidrogenação do CO>sub<2>/sub< em baixas pressões

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