Dual‐Ionically Bound Single‐Site Rhodium on Porous Ionic Polymer Rivals Commercial Methanol Carbonylation Catalysts

Abstract

porous organic polymers (POPs) connected through strong autologous covalent bonds from vinyl-polymerization are emerging as a family of advanced materials advantageous to MOFs, because of a relatively high thermal stability of the skeleton, a hierarchical porosity, as well as the structural diversity. [4] In addition, the ligands [4] or the functional sites [5] in POPs can serve as strong anchoring sites for different metals with great tunability of the metal properties via different preparation methods, being more suitable for cataly sis. It has been believed that the chemical bond between metal species and POPs can be a coordination or an ionic bond, and the latter is generally more stable particularly under harsh reaction conditions. In this context, an effective method to create strong ionic bond is by the immobilization of the ionic active sites onto a new type of POPs with charged skeleton balanced by counterions, coined herein as porous ionic polymers (PIPs). [5] Thanks to the strong bonding and the ionic nature, the resultant single-site metal catalysts can well inherit both the advantages of homo-and heterogeneous processes, i.e., the high activity of the former and the catalyst robustness of the latter. Herein, we first briefly introduce the preparation approaches for porous organic polymers and the corresponding strategies for heterogenization of homogeneous metallic catalysts, and then exemplify a PIP hosted single-site rhodium catalyst (Rh 1 /PIP) for vapor-phase methanol carbonylation, and its excellent performance shows a promising prospect in this exciting field. POPs Polymerized by Vinyl-Based MonomersDifferent synthetic strategies have been developed to prepare POPs. [3,6] The widely used hard or soft-templates are supposed to be removed completely, requiring a highly complicated and energy-consuming procedure. [3] Moreover, the residual metals (Cu, Ni, etc.) as polymerization catalysts for Sonogashira, [7,8] Click, [9] and Yamamoto reactions [10] usually show negative impacts on the catalytic performance of POPs. Contrarily, the polymerization process of vinyl-based monomers is an exception, which can not only avoid the residue of templates and metals, but also offer excellent yields (near 100%) and simple operation. [11] Novel porous polymers can serve as self-supporting solid carriers and provide abundant coordination or charged sites for single-site metals, and thus are emerging as advanced functional materials in heterogeneous catalysis for various transformations traditionally catalyzed by homogeneous systems. A brief overview of the development of this heterogenization given, including the recent advances regarding electrovalent bonds by employing charged supports represented by porous ionic polymers (PIPs), which is exemplified herein with a novel single-site Rh 1 /PIP catalyst, featuring a new active site [Rh(CO)I 3 ] 2− dual-ionically bound onto a quaternary phosphonium cationic framework polymer, different from the single-ionically bound [Rh(CO) 2 I 2 ] − in previous studies. Such a u...

Stabilizing Isolated Rhodium Cations by MFI Zeolite for Heterogeneous Methanol Carbonylation

“…To our surprise, Rh@ZSM-5 exhibited a state of the art TOF value (3950 mol acetyl /(mol Rh h)) at a low reaction temperature of 423 K, higher than that achieved on heterogeneous Rh 1 /PIP (3500 mol acetyl /(mol Rh h) at 468 K) or a homogeneous Rh coordination sphere with the mononuclear complex of a dissymmetric diphosphine ligand (3212 mol acetyl /(mol Rh h) at 443 K). It should be mentioned that the high TOF value of Rh@ZSM-5 is achieved at a moderate Rh loading of 0.95 wt %, in significant contrast to the low Rh loading of 0.28 wt % in Rh 1 /PIP, offering a good space–time productivity of ∼0.4 mol acetyl /(g cat h). To our knowledge, Rh@ZSM-5 is the most active Rh-based catalyst for methanol carbonylation, in both homogeneous and heterogeneous systems.…”

“…More importantly, the key issues of catalytic deactivation and separation in homogeneous systems remain unsolved. ,, In this context, the heterogenized carbonylation catalysts are coming into focus, and some alternative routes have been developed thereupon. UOP and Chiyoda have developed a heterogeneous carbonylation process without the addition of an alkali iodide salt as the promoter, called Acetica, employing a Rh catalyst complexed on a poly­(vinylpyridine) resin. , Recently, single Rh sites immobilized on porous organic polymers (POPs) , and porous ionic polymers (PIPs) were reported to show unprecedented activity in methanol carbonylation, rivaling commercial homogeneous Rh catalysts.…”

Selective Methanol Carbonylation to Acetic Acid on Heterogeneous Atomically Dispersed ReO4/SiO2 Catalysts

“…Supported transition metal heterogeneous catalysts have shown promise for methanol carbonylation. , However, most processes still rely on halide additives, and/or the reported reactivity, selectivity, or stability is lower than existing homogeneous processes. , For example, atomically dispersed iridium (Ir) on active carbon (AC) was shown to have comparable reactivity and selectivity to that of the analogous homogeneous catalyst, but its rapid deactivation precludes industrial viability. , Co-deposition of lanthanum (La) resulted in a 3-fold increase in reactivity compared to Ir/AC with an acetyl selectivity of 99% that remained stable for more than 1 month. , Analogously, atomically dispersed rhodium (Rh) on porous organic polymers (POPs) has also shown good performance for methanol carbonylation, with catalyst stability for 400 h on stream. − These heterogeneous catalytic processes still use halides and water, which minimizes the potential benefit over the already commercialized homogeneous processes.…”

Quaternary phosphonium polymer-supported dual-ionically bound [Rh(CO)I3]2– catalyst for heterogeneous ethanol carbonylation

“…The previously tentatively proposed Rh dianion [Rh(CO)I3] 2- [30], immobilized by two cationic P sites, displayed much higher heterogeneous methanol carbonylation activity (TOF = 3500 h -1 , 3.5 MPa, 468 K) than that of the reported "Acetica TM " system containing the [Rh(CO)2I2] -species (TOF = 1700 h -1 , 4.0 MPa, 463 K), which might indicate that the quaternary phosphonium polymer favors the generation of [Rh(CO)I3] 2- [27,28]. Thus, herein, by using the quaternary phosphonium polymer as a support, a newly-synthesized analogous quaternary phosphonium polymer supported catalyst, Rh-TPISP, is studied in-depth.…”