Isoreticular Metal–Organic Frameworks Confined Mononuclear Ru-Hydrides Enable Highly Efficient Shape-Selective Hydrogenolysis of Polyolefins

Abstract

Upcycling nonbiodegradable plastics such as polyolefins is paramount due to their ever-increasing demand and landfills after usage. Catalytic hydrogenolysis is highly appealing to convert polyolefins into targeted value-added products under mild reaction conditions compared with other methods, such as high-temperature incineration and pyrolysis. We have developed three isoreticular zirconium UiO-metal–organic frameworks (UiO-MOFs) node-supported ruthenium dihydrides (UiO-RuH 2 ), which are efficient heterogeneous catalysts for hydrogenolysis of polyethylene at 200 °C, affording liquid hydrocarbons with a narrow distribution and excellent selectivity via shape-selective catalysis. UiO-66-RuH 2 catalyzed hydrogenolysis of single-use low-density polyethylene (LDPE) produced a C12 centered narrow bell-shaped distribution of C8–C16 alkanes in >80% yield and 90% selectivity in the liquid phase. By tuning the pore sizes of the isoreticular UiO-RuH 2 MOF catalysts, the distribution of the products could be systematically altered, affording different fuel-grade liquid hydrocarbons from LDPE in high yields. Our spectroscopic and theoretical studies and control experiments reveal that UiO-RuH 2 catalysts enable highly efficient upcycling of plastic wastes under mild conditions owing to their unique combination of coordinatively unsaturated single-site Ru-active sites, uniform and tunable pores, well-defined porous structure, and superior stability. The kinetics and theoretical calculations also identify the C–C bond scission involving β-alkyl transfer as the turnover-limiting step.

Chemical Upcycling of Polyolefin Plastics Using Structurally Well-defined Catalysts

“…Three ordered zirconium UiO-metal–organic frameworks (UiO-MOFs)-supported Ru dihydrides (UiO-RuH 2 ) catalysts, UiO-66-RuH 2 , UiO-67-RuH 2 , and UiO-68-RuH 2 with pore sizes of 5.1, 6.8, 8.1 Å, were synthesized to catalyze PO hydrogenolysis reactions. 67 The product distributions from hydrogenolysis of PE ( M n : ∼1700 Da, M w : ∼4000 Da), depicted in Figure 10 a, showed a noticeable shift from lighter, narrower to heavier, broader when the MOF pore sizes are increased from 5.1 to 8.1 Å. Although methane was always the dominant component in gaseous products regardless of the pore size of MOFs, UiO-68-RuH 2 gave an excellent yield of 94% of liquid products.…”

“…Reaction conditions: 0.60 g of polymer substrate, ∼4 μmol of Ru, 200 °C, 35 bar H 2 , and 72 h. (b) Hydrogenolysis of postconsumer single-use LDPE plastic bags or droppers by UiO-Ru of different pore sizes to afford liquid and gaseous products along with % selectivity of liquid products in several alkane ranges. Reaction conditions: 2.4 g of polymer substrate, ∼16 μmol of Ru, 200 °C, 35 bar H 2 , and 20 h. Reproduced with permission from ref ( 67 ). Available under a CC-BY-NC-ND 4.0 license.…”

Metal–Organic Framework-Supported Mono Bipyridyl–Iron Hydroxyl Catalyst for Selective Benzene Hydroxylation into Phenol

“…As porous and tunable molecular materials, metal–organic frameworks (MOFs) have garnered significant attention for developing robust single-site heterogeneous catalysts for diverse applications. − In particular, UiO-MOFs, constructed from Zr 6 (μ 3 -O) 4 (μ 3 –OH) 4 secondary building units (SBUs) or nodes and linear dicarboxylate bridging linkers, offer excellent thermally and chemically robust platforms. ,− The inherent capability of MOFs to sustain postsynthetic modification allows the functionalization of organic linkers of MOFs, which leads to the formation of single-site base-metal catalysts upon metalation. ,− Furthermore, MOF-supported single-site catalysts offer a blend of advantages from homogeneous catalysts, including uniform distribution of active sites, and heterogeneous counterparts, such as robustness and easy catalyst recycling. ,− Pan et al recently reported nitrogen atom-ligated single-site Fe-catalysts, in which increasing the Fe–N coordination number enhanced the benzene oxidation activity . We surmised that bipyridyl iron species confined within a porous MOF could be highly robust and selective heterogeneous catalysts for hydroxylation of benzene via active-site isolation.…”

Mechanochemical Encapsulation of Enzymes into MOFs for Photoenzymatic Enantioselective Catalysis

“…These results confirmed the successful synthesis of photobiocatalysts (Figure S12–S13). − To further unveil the position and distribution of WGL, isothiocyanate fluorescein isothiocyanate (FITC)-labeled WGL and confocal laser scanning microscopy (CLSM) was performed, which showed that WGL was uniformly loaded inside the UiO-67 materials (Figure c and Figure S14). Further, the 3D view CLSM images of FITC-tagged WGL@UiO-67-Ru/Cu are shown in Figure d and Figure S15–S17.…”