Nuclearity and Host Effects of Carbon‐Supported Platinum Catalysts for Dibromomethane Hydrodebromination

Abstract

could be approached by engineering both the geometry and the electronic properties of the active phase at the nanoscale. [2,3] However, in contrast to well-defined homogeneous catalysts, establishing structureperformance relations and identifying the active sites in heterogeneous systems is challenging due to the inherent material complexity. [3,4] In this regard, employing single-atom heterogeneous catalysts (SACs), containing isolated atoms in discrete chemical environments is an effective approach to enable fundamental and mechanistic studies. [3][4][5][6][7] Beyond this, SACs often exhibit unique performance in diverse reactions due to their high degree of metal dispersion, tunable electronic properties, and unsaturated coordination environments of the active centers in tailored host materials. [7][8][9][10][11][12][13][14] In this regard, the first step in the development of a catalyst design strategy entails a detailed assessment on the impact of metal nuclearity and host effects, from single atoms with defined environments to size-controlled nanoparticles, on reactivity patterns for a given application. [15][16][17] A prominent class of reactions, widely used in numerous industrial processes, are hydrogenations, [18][19][20] which are commonly carried out over supported nanoparticles of precious metals with high sensitivity to their specific ensemble design. [21][22][23][24][25][26][27] An example of high practical relevance is the hydrodebromination of dibromomethane (CH 2 Br 2 ) into bromomethane (CH 3 Br), an important transformation for the industrial realization of bromine-mediated natural gas upgrading technologies into chemicals and fuels. [28][29][30] Therein, limited progress has been made toward selective hydrodebromination, where carbon losses in the form of CH 4 and coke represent a major challenge. [30,31] A recent study evaluated the performance of SiO 2 -supported nanoparticle-based (NP-based) metal catalysts (1 wt% of Fe, Co, Ni, Cu, Ru, Rh, Ag, Ir, Pt). Therein, at comparable reaction conditions, iron-, cobalt-, copper-, and silver-based catalysts displayed CH 2 Br 2 conversion levels of 4-7%, showing consistency with the reported poor hydrodebromination ability of these elements. [30] Among the platinum group metals, selective CH 2 Br 2 hydrodebromination to CH 3 Br was reported over Ru/SiO 2 (up to 96%, Table 1), whereas the CH 3 Br selectivity over Rh/SiO 2 (<48%), Ir/SiO 2 (<40%), and Pt/SiO 2 (23%) wasThe identification of the active sites and the derivation of structure-performance relationships are central for the development of high-performance heterogeneous catalysts. Here, a platform of platinum nanostructures, ranging from single atoms to nanoparticles of ≈4 nm supported on activated-and N-doped carbon (AC and NC), is employed to systematically assess nuclearity and host effects on the activity, selectivity, and stability in dibromomethane hydrodebromination, a key step in bromine-mediated methane functionalization processes. For this purpose, catalytic evaluation is coupled to ...

Generalizing Performance Equations in Heterogeneous Catalysis from Hybrid Data and Statistical Learning

“…Catalytic gas-phase hydrodehalogenations is a family of reactions in which halogen elimination from an organic compound is followed by hydrogen addition. The selective transformation of CH 2 X 2 into CH 3 X is of particular interest, since it is an important step in halogen-mediated natural gas upgrading processes, − although it presents selectivity issues. In the reaction mechanism, as shown in Figure S1 in the SI, the target CH 3 X is formed by the removal of a single halogen and the addition of an H atom.…”

“…In order to develop a robust framework for the deployment of SL with the aim to obtain reactivity equations of heterogeneous catalysts, we have used the hydrodehalogenation of CH 2 X 2 (X = Br, Cl) and compared them to MK­(DFT) models. This transformation is a key step in halogen-mediated methane upgrading processes and clearly displays the selectivity issues of the metal catalysts. − By combining the descriptor identification from PCA and BMS, we present a unique equation search for the reaction rate, CH 2 X 2 conversion, and selectivity to different products, thus compiling the performance of the metal catalyst in a generalized form (procedure depicted in Figure ). Our approach links experimental and theoretical data and sets a robust methodology that could be extrapolated to other heterogeneously catalyzed reactions.…”

Carbon‐Supported Bimetallic Ruthenium‐Iridium Catalysts for Selective and Stable Hydrodebromination of Dibromomethane

“…The stability of platinum and iridium nanoparticles, which mainly generate CH 4 (>47 % selectivity), initiated further investigations aiming to improve the selectivity while maintaining the high durability of these metals. A recent study systematically assessed the effect of various platinum nanostructures supported on activated‐ (AC) or nitrogen‐doped (NC) carbon, to assess metal size and host effects on performance [5a] . Whereas the unparalleled selectivity to CH 3 Br (<98 %) over the NC‐supported platinum single atoms was reported, catalyst deactivation remained a major concern.…”

“…A recent study systematically assessed the effect of various platinum nanostructures supported on activated‐ (AC) or nitrogen‐doped (NC) carbon, to assess metal size and host effects on performance. [5a] Whereas the unparalleled selectivity to CH 3 Br (<98 %) over the NC‐supported platinum single atoms was reported, catalyst deactivation remained a major concern. Exposure to relevant hydrodebromination conditions ( T =523 K, P =1 bar, H 2 : CH 2 Br 2 =4 : 1) promotes agglomeration of the single atoms into nanoparticles and fouling due to coking, enhanced by the insufficient durability of the NC carrier.…”

Controlled synthesis of Bi- and tri-nuclear Cu-oxo nanoclusters on metal–organic frameworks and the structure–reactivity correlations

“…The establishment of structure-reactivity correlations between the active centres and catalytic properties is regarded as an important platform for the rational design and engineering of more superior and selective systems. In recent years, various catalytic materials with atomic precision have been fabricated to achieve exciting performance in different applications, [9][10][11] such as [Cu 3 (μ-O) 3 ] 2+ supported on MOR zeolite for the selective oxidation of methane to methanol by Lercher et al 12 , and the engineering of MIL-101(Ti)-based Cu 2 species as artificial monooxygenase by Lin et al 13 The catalytic characteristics of NCs can generally be correlated to nuclearity (number of atoms), 15 electronic (HOMO-LUMO work functions and binding affinities) 16 and geometric properties (morphology and coordination environments) 17 of the active sites. Some reaction mechanisms are governed by the adsorption configurations of the substrates.…”