Showing papers by "Philippe Serp published in 2022"

Multifunctional Catalytic Properties of Pd/CNT Catalysts for 4‐Nitrophenol Reduction

Abstract: Carbon nanotubes are arousing real interest in catalysis, either as catalyst support or as catalyst itself. In this work, the influence of CNT doping (O, N, S) on the catalytic performance of CNT and Pd/CNT catalysts have been investigated in the reduction of 4‐nitrophenol both under H2 or using NaBH4 as a hydride source. The morphology, composition, particle size and crystallinity of the materials were investigated by various techniques including HRTEM, STEM, XPS, Raman spectroscopy and XRD. Among the CNT carbocatalysts, only N‐CNT is active for 4‐nitrophenol reduction at room temperature, and only in the presence of NaBH4. As far as supported Pd catalysts are concerned, the nature of the support influences the Pd nanoparticle location (confinement), the Pd nanoparticles/Pd single atoms ratio and the extent of H‐spillover, three catalyst features that directly affect the catalytic activity. The best combination of Pd nanoparticles/Pd single atoms ratio, H‐spillover and confinement for 4‐nitrophenol reduction using NaBH4, is found in Pd/O‐CNT catalysts, while for reactions performed under H2, Pd/N‐CNT presents the best combination.

Solvent‐Free Hydrogenation of Squalene Using Parts per Million Levels of Palladium Supported on Carbon Nanotubes: Shift from Batch Reactor to Continuous‐Flow System

Abstract: Abstract The transition from batch catalytic processes to continuous flow processes requires highly active and stable catalysts that still need to be developed. The preparation and characterization of catalysts where palladium single atoms and nanoparticles are simultaneously present on carbon nanotubes were recently reported by us. These catalysts are considerably more active than commercial or previously described catalysts for the liquid phase hydrogenation of terpenes. Herein is shown that under solvent‐free conditions, squalene (SQE) could be converted into squalane (SQA,>98 %) using only 300 ppm of Pd in less than 1.4 h at 20 bar H2 and 120 °C. Catalyst stability was assessed in a lab‐scale flow reactor, and long‐term experiments led to turnover number (TON) higher than 300000 without any detectable loss in the activity. Then, the implementation of this catalyst in a commercial intensified continuous‐flow milli‐reactor pilot was achieved. High purity SQA (>98 %) could be obtained by continuous hydrogenation of solvent‐free SQE at 180 °C and 30 bar H2 with a contact time below 15 min. A production capacity of 3.6 kg per day of SQA could be obtained with an effective reactor volume (V R) of 43.2 mL for this complex 3 phase reaction. Large‐scale production can now be foreseen thanks to seamless scale‐up provided by the continuous flow pilot supplier.

Epsilon Cobalt Nanoparticles as Highly Performant Catalysts in Cinnamaldehyde Selective Hydrogenation

Abstract: Epsilon cobalt nanoparticles are underexplored in catalysis due to the fact that they are accessible only through wet-chemical approaches, which employ ligands as stabilizing agents. Ligands may play a significant role in determining the structure and catalytic performances of nanoparticles, which complicates their comparison in catalysis. Here, we present catalytic performances in cinnamaldehyde hydrogenation of freestanding and few-layer graphene-supported ε-Co nanoparticles and hexagonal close-packed (hcp)-Co nanorods, which are stabilized by the same ligands. We show that while hcp-Co nanorods exposing a majority of {112̅0}-type facets are the most active, the supported spherical ε-Co nanoparticles combine high activity and excellent selectivity for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. The concentration-dependent ligand conformation on the surface of the nanostructures influences their catalytic performances, with higher concentrations favoring both activity and selectivity to cinnamyl alcohol. These results should incite the interest in the implementation of ε-Co nanoparticles in other catalytic reactions where the cobalt crystal structure may play an important role.

Introduction to Supported Metal Single Atom Catalysis

Abstract: The main purpose of this introductory chapter is to: (i) familiarize non-experts in the field with this type of catalysis, and (ii) draw the attention of experts to related and complementary fields of which a basic knowledge may be necessary for a good understanding of this type of catalysis. More specifically, we intend to: (i) introduce the key aspects of catalysis with supported metal single-atom catalysts, (ii) discuss the drawing together of closely aligned topics, and (iii) acknowledge the challenges and possible opportunities around the area.

Preparation of Supported Metal Single‐Atom Catalysts on Carbon Supports

Abstract: In this chapter, we review the most representative synthesis methods for the preparation of single-atom catalysts on carbon supports. We identify key parameters in each of the different protocols and address some of the stabilization mechanisms. Special attention is paid to the correlation between the structure and the catalytic properties of the different active sites (M–C, M–N–C, etc.). Both technical and theoretical aspects of the synthetic approaches are discussed with the intention to give an insight into the advantages and drawbacks when choosing a specific method.

Preparation of Supported Metal Single‐Atom Catalysts on Metal Oxides and Hydroxides

Abstract: During the last decade, great attention has been devoted to supported metal single-atom catalysts (SACs), due to the maximal metal utilization and the unique reactivity of such materials. The preparation of high-loading, stable isolated metal atoms with the desired local environments remains the main challenge for the industrial application of SACs. In this chapter, we discuss in detail the most representative methods for the preparation of SACs on oxide and hydroxide supports to give to the reader a complete idea of the different steps of each procedure employed and the final stability of the deposited single atoms. Moreover, we focus our attention on the “bottom-up” methods, which represent a facile and universal route for the direct preparation of SACs on metal oxides and hydroxides.