Magnetite-supported palladium single-atoms do not catalyse the hydrogenation of alkenes but small clusters do

Abstract

The activity of supported noble metal catalysts strongly depends on the particle size. The ultimate small-size limit is the single-atom catalyst (SAC), which maximizes the catalytic efficiency in the majority of the examples. Here, we investigate the catalytic behavior of Pd SACs supported on magnetite nanoparticles and we unambiguously demonstrate that Pd SACs are absolutely inactive in the hydrogenation of various alkene substrates. Instead, Pd clusters of low atomicity exhibit outstanding catalytic performance.Postprint (author's final draft

The Multifaceted Reactivity of Single‐Atom Heterogeneous Catalysts

“…Although this has well-known limitations for evaluating relative activity because only af raction of the metal atoms in NPs and even in SACs may be contributing to this,t he quantification of the actual number of active atoms is beyond current experimental capabilities.V ariation of the metal speciation is widely approached by reducing the amount of metal in the catalyst and may be reported in terms of the loading, size of the species deposited, or surface coverage.A nalysis of the reported trends reveals that they are well-described by three characteristic scenarios ( Figure 4). [73] Af ourth scenario can be envisaged in which the activity of SAs is non-negligible but small NPs are optimal, in which case the activity would not drop to zero at low concentrations;h owever, no such result was identified in our literature analysis. [69,70] On the other hand, if NPs can also catalyze the reaction (SAs > NPs) the activity will rise more gradually with increasing dispersion until it reaches ap lateau as the metal species tend toward SAs.…”

“…NPs) the activity may initially increase as the metal content is reduced because of higher dispersion, before falling sharply to close to zero when metal clusters are no longer present in the sample. [73] Af ourth scenario can be envisaged in which the activity of SAs is non-negligible but small NPs are optimal, in which case the activity would not drop to zero at low concentrations;h owever, no such result was identified in our literature analysis.…”

“…Trends in relative tof (based on the total metal content and normalized to the maximum value) upon reducing the atomic populationo f metal NPs (&)t oSAs (~). a nd[73],respectively. Adapted with permission of refs [69,71].…”

Highly water-dispersible magnetite-supported Pd nanoparticles and single atoms as excellent catalysts for Suzuki and hydrogenation reactions

“…On the other hand, the sample Fe 3 O 4 dpa@Pd 0.1 , which only contains Pd single atoms, exhibits a Pd(0) component at a signicantly higher binding energy value (335.8 vs. 335.2 to 335.3 eV), which suggests that there is an electronic transfer from the Pd single atoms to the Fe 3 O 4 support, in accordance with previous reports. 16,17 Catalytic studies Suzuki-Miyaura reaction. Palladium-catalyzed Suzuki-Miyaura cross-coupling is a well-known process for the synthesis of biaryls using aryl halides with arylboronic (Scheme 2) acids; it has many applications in agrochemicals, natural products and pharmaceutical intermediates.…”

Remarkable Carbon Dioxide Hydrogenation to Ethanol on a Palladium/Iron Oxide Single‐Atom Catalyst

“…They are referred to as 0.1Pd/Fe 3 O 4 ,0 .4Pd/Fe 3 O 4, and 3Pd/Fe 3 O 4 ,r espectively.T he different Pd loading values were selected according to Ref. [13] to obtain catalysts containing different Pd particle sizes. In particular,0 .1Pd/Fe 3 O 4 containse xclusively Pd single atoms ( Figure 1a and Figure S1 in the Supporting Information), 0.4Pd/Fe 3 O 4 contains small Pd clusters of (1.2 AE 0.2) nm (Figure 1b), and 3Pd/Fe 3 O 4 contains Pd nanoparticles of (4.3 AE 0.4) nm ( Figure 1c).…”