Constructing Efficient Single Rh Sites on Activated Carbon via Surface Carbonyl Groups for Methanol Carbonylation

Abstract

Heterogeneous single-metal-site catalysts have been drawing increasing interests in the field of academy and industry because of the comparable catalytic activity with homogeneous catalyst and easy separation.Here, an efficiently heterogeneous single-site Rh catalyst on activated carbon (Rh 1 /AC) was constructed, which performs three times activity than the corresponding homogeneous catalyst for methanol carbonylation. Experimental data reveals that the apparent activation energy on the Rh 1 /AC catalyst is 0.91 eV, far less than 1.54 eV of its homogeneous counterpart. Ex situ EXAFS confirms the molecular configuration of a single Rh site. DFT calculation demonstrates that the electron-donating carbonyl group on the surface of the support possesses the precedence to accommodate the singlesite Rh ions. Furthermore, difference charge density verifies that the coordinative bond between a single metal ion and a carbonyl group enhances the electronic density of the central Rh atom, consequently lowering the energy barrier of the rate-determining step of CH 3 I oxidative addition. Together with the atomic dispersion, as well as the electronic interaction between a single Rh ion and carbonyl groups, the Rh 1 /AC catalyst performs superior activity than homogeneous systems.

Iodide-Coordinated Single-Site Pd Catalysts for Alkyne Dialkoxycarbonylation

“…41,42 Therefore, the atomically dispersed Pd ions were assigned a molecular configuration of [Pd(CO)I 4 (OAC)] 2− , where (OAC) represents carbonyl groups on the surface of the AC support. 6,43 Compared with Ir or Au NPs, for which NPs larger than 10 nm were very difficult to disperse, 9,17,18 large Pd NPs with a size of approximately 16 nm were surprisingly readily dispersed. To evaluate the atomic dispersion of Pd NPs at different reaction times, systematic characterizations, including XRD, TEM, HAADF−STEM, XPS, in situ DRIFT, and in situ iPEPICO spectroscopy, were performed.…”

“…Moreover, wavelet transform (WT) contour plots of the Pd/AC and Pd 1 /AC samples also confirmed the backscattering of Pd NPs with k values concentrated at 10.0 Å –1 in the Pd/AC catalyst and the single Pd ions in the Pd 1 /AC catalyst with k values concentrated at 11.4 Å –1 in both radial distance and k -space resolution (Figure S5). , Therefore, the atomically dispersed Pd ions were assigned a molecular configuration of [Pd­(CO)­I 4 (OAC)] 2– , where (OAC) represents carbonyl groups on the surface of the AC support. , Compared with Ir or Au NPs, for which NPs larger than 10 nm were very difficult to disperse, ,, large Pd NPs with a size of approximately 16 nm were surprisingly readily dispersed.…”

“…Developing a metal catalyst with 100% atom efficiency is the holy grail of academic and industrial catalysis research. Heterogeneous single-metal-site catalysts (HSMSCs) have attracted considerable attention since their emergence. , The unique coordination environment of a single-site catalyst is crucial to achieving excellent performance. − Constructing this kind of catalyst via a feasible and practical fabrication method is challenging. Atomic dispersion of nanoparticles (NPs) is used not only to prepare HSMSCs but also to redisperse agglomerated or sintered metal NPs. − One of the most pressing challenges is overcoming the Ostwald ripening process, − which is manifested as the growth of large particles at the expense of smaller particles.…”

Sulfur Poisoning on Rh Nanoparticles but Sulfur Promotion on Its Single-Site Catalyst for Carbonylation

“…In-situ diffuse re ectance infrared Fourier transformation spectroscopy on Rh 1 /AC catalyst in S-feed showed a peak at ~1775 cm -1 ascribed to acetyl species, appearing after reaction for 20 min, earlier than that in the normal feed at 25 min (Extended Data Figure 14a-b 22,[27][28][29][30] (Figure 3 and Extended Data Figure 18).…”

Heterogenisation of a carbonylation catalyst on dispersible microporous polymer nanoparticles

“…17,18 Another approach to minimise problems with solubility at low water concentration is to heterogenise the catalyst by immobilisation on a solid support. 5,16,19 A range of support materials that bind the Rh catalyst directly through a covalent interaction have been investigated, including inorganic oxides, 20,21 zeolites, [22][23][24][25] polymers, [26][27][28][29][30][31] carbon 32 and covalent triazine frameworks. 33 Many of these systems exhibit reaction rates slower than that of the homogeneous process, likely due, in part, to the covalent tethering of the catalyst, which modifies the first coordination sphere of the Rh complex.…”