Hollow-Shell-Structured Mesoporous Silica-Supported Palladium Catalyst for an Efﬁcient Suzuki-Miyaura Cross-Coupling Reaction

: The construction of a high stability heterogeneous catalyst for privileged common catalysis is a beneﬁt in regard to reuse and separation. Herein, a palladium diphenylphosphine-based hollow-shell-structured mesoporous catalyst ( HS@PdPPh 2 @MSN ) was prepared by immobilizing bis((diphenylphosphino)ethyltriethoxysilane)palladium acetate onto the inner wall of a mesoporous organicsilicane hollow shell, whose surface was protected by a –Si(Me) 3 group. Electron microscopies conﬁrmed its hollow-shell-structure, and structural analyses and characterizations revealed its well-deﬁned single-site active species within the silicate network. As presented in this study, the newly constructed HS@PdPPh 2 @MSN enabled an efﬁcient Suzuki-Miyaura cross-coupling reaction for varieties of substrates with up to 95% yield in mild conditions. Meanwhile, it could be reused at least ﬁve times with good activity, indicating its excellent stability and recyclability. Furthermore, the cost-effective and easily synthesized HS@PdPPh 2 @MSN made it a good candidate for employment in ﬁne chemical engineering.


Synthesis and Structural Characterization of the Hollow-Shell Catalyst
Hollow-shell-structured (PPh 2 ) 2 Pd(OAc) 2 -functionalized mesoporous silica nanoparticles, abbreviated as HS@PdPPh 2 @MSN (3), were synthesized through a simple postgrafting-complexation three-step procedure, as shown in Scheme 1. The first step was the co-condensation of tetraethoxysilane (TEOS) and 1,2-bis(triethoxysilyl)ethane, followed by the modification of hexamethyldisilazane (HMDS) leading to silylated coreshell-structured nanoparticles Me@SiO 2 @NPs. The second step was the post grafting of diphenyl (2-(triethoxysilyl)ethyl)phosphane within the inner surface of the silylated Me@HS@MSN (1), which was obtained by an etching process in toluene for 12 h under refluxing condition. The third step was the direct complexation of the immobilized diphenyl(2-(triethoxysilyl)ethyl)phosphane with Pd(OAc) 2 in the cavity of the hollow-shellstructured mesoporous silica and producing of the coarse catalyst 3, which was subjected to a Soxhlet extraction to remove the unreactive materials providing its pure form as a gray powder. For comparison, an analog (catalyst 3 ) of catalyst 3, which was unprotected by hexamethyldisilazane, was also prepared by a similar procedure (see Supplementary Information in the Experimental Section, and Figures S1-S2). The thermal gravimetric (TG) analysis revealed that the PdPPh 2 -loadings in catalyst 3 was 97.47 mg (0.92 mmol) per gram catalyst, which was in accordance with the mole amount of Pd-loadings (1.03 mmol (110.6 mg) per gram catalyst 3) detected by using an inductively coupled plasma optical emission spectrometer (ICP-OES) analysis.
The solid-state 13 C cross-polarization (CP)/magic angle spinning (MAS) NMR spectroscopy was collected to confirm the incorporation of the (PPh 2 ) 2 Pd(OAc) 2 -functionality within the inner sphere of the hollow shell of three. As shown in Figure 1, the strong carbon signals around 5.6 ppm belonged to the -SiCH 2 CH 2 Si-groups for the ethylene-bridged moiety in catalyst 3, suggesting its ethylene-bridged network of the organosilicate shell. Especially, the characteristic peaks at 26.9 and 188.5-174.3 ppm for the carbon atoms of -CH 2 P and -PC 6 H 5 groups were presented in catalyst 3, similar to those of its homogeneous counterpart [50]. Further, in the spectrum of three, the strong signals for the carbon atoms of the aromatic ring could be observed clearly, while all these peaks were absent in the spectrum of one, revealing that three had the same well-defined single-site active species as its homogeneous counterpart. Moreover, its solid-state 31 P CP MAS spectrum (Figure 2) also demonstrated the same well-defined single-site active species as its homogeneous counterpart [51]. The solid-state 13 C cross-polarization (CP)/magic angle spinning (MAS) NMR spectroscopy was collected to confirm the incorporation of the (PPh2)2Pd(OAc)2-functionality within the inner sphere of the hollow shell of three. As shown in Figure 1, the strong carbon signals around 5.6 ppm belonged to the -SiCH2CH2Sigroups for the ethylenebridged moiety in catalyst 3, suggesting its ethylene-bridged network of the organosilicate shell. Especially, the characteristic peaks at 26.9 and 188.5-174.3 ppm for the carbon atoms of -CH2P and -PC6H5 groups were presented in catalyst 3, similar to those of its homogeneous counterpart. [50] Further, in the spectrum of three, the strong signals for the carbon atoms of the aromatic ring could be observed clearly, while all these peaks were absent in the spectrum of one, revealing that three had the same well-defined single-site active species as its homogeneous counterpart. Moreover, its solid-state 31 P CP MAS spectrum (Figure 2) also demonstrated the same well-defined single-site active species as its homogeneous counterpart [51].  The solid-state 13 C cross-polarization (CP)/magic angle spinning (MAS) NMR spectroscopy was collected to confirm the incorporation of the (PPh2)2Pd(OAc)2-functionality within the inner sphere of the hollow shell of three. As shown in Figure 1, the strong carbon signals around 5.6 ppm belonged to the -SiCH2CH2Sigroups for the ethylenebridged moiety in catalyst 3, suggesting its ethylene-bridged network of the organosilicate shell. Especially, the characteristic peaks at 26.9 and 188.5-174.3 ppm for the carbon atoms of -CH2P and -PC6H5 groups were presented in catalyst 3, similar to those of its homogeneous counterpart. [50] Further, in the spectrum of three, the strong signals for the carbon atoms of the aromatic ring could be observed clearly, while all these peaks were absent in the spectrum of one, revealing that three had the same well-defined single-site active species as its homogeneous counterpart. Moreover, its solid-state 31 P CP MAS spectrum (Figure 2) also demonstrated the same well-defined single-site active species as its homogeneous counterpart [51].    Additionally, the solid-state 29 Si MAS NMR spectroscopy was collected and confirmed the organosilicate network and composition of catalyst 3. As shown in Figure 3, there were a few differences among the precursors (1 and 2) and catalyst 3 in the solidstate 29 Si MAS NMR spectra, and two typical signals (where Q signals were attributed to inorganosilica, while T signals corresponded to organosilica) were distributed broadly  Additionally, the solid-state 29 Si MAS NMR spectroscopy was collected and confirmed the organosilicate network and composition of catalyst 3. As shown in Figure 3, there were a few differences among the precursors (1 and 2) and catalyst 3 in the solid-state 29 Si MAS NMR spectra, and two typical signals (where Q signals were attributed to inorganosilica, while T signals corresponded to organosilica) were distributed broadly from −40 to −150 ppm. As compared to those typical isomer shift values in the literature [9], the T 2 signal of the T-series at 57.1 ppm presented the {(R-Si(OSi) 2 (OH))} or {(R-Si(OSi) 2 (CH 2 CH 3 ))}, where R = alkyl-linked PPh 2 Pd(OAc) 2 in three and/or ethylene-bridged group in one and two, and the strongest T 3 signal of the T-series at −67.6 ppm suggested R-Si(OSi) 3 organosilicate species. In the silica wall of the hollow-shell silica, the intensity of T signals was markedly higher than that of Q signals, and the other three Q signals at −91, −102, and −111 ppm were attributed to Q 2 ((Me 3 Si-O) 4 Si), Q 3 (Si(OSi) 3 (OH)), and Q 4 (Si(OSi) 4 ) species coming from the TEOS precursor. The above results demonstrated that the incorporated precursors were covalently converted within its organosilica network. Additionally, the solid-state 29 Si MAS NMR spectroscopy was collected and confirmed the organosilicate network and composition of catalyst 3. As shown in Figure 3, there were a few differences among the precursors (1 and 2) and catalyst 3 in the solidstate 29 Si MAS NMR spectra, and two typical signals (where Q signals were attributed to inorganosilica, while T signals corresponded to organosilica) were distributed broadly from −40 to −150 ppm. As compared to those typical isomer shift values in the literature [9], the T 2 signal of the T-series at 57.1 ppm presented the {(R-Si(OSi)2(OH))} or {(R-Si(OSi)2(CH2CH3))}, where R = alkyl-linked PPh2Pd(OAc)2 in three and/or ethylenebridged group in one and two, and the strongest T 3 signal of the T-series at −67.6 ppm suggested R-Si(OSi)3 organosilicate species. In the silica wall of the hollow-shell silica, the intensity of T signals was markedly higher than that of Q signals, and the other three Q signals at −91, −102, and −111 ppm were attributed to Q 2 ((Me3Si-O)4Si), Q 3 (Si(OSi)3(OH)), and Q 4 (Si(OSi)4) species coming from the TEOS precursor. The above results demonstrated that the incorporated precursors were covalently converted within its organosilica network. The morphology and ordered mesostructure of three were further investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption-desorption measurements. As shown in Figure 4, the nitrogen adsorptiondesorption isotherm of three showed a typical type IV isotherm with an H1 hysteresis loop and a visible step at P/P0 = 0.45-0.95 demonstrating its mesoporous structure. The pore size distribution of catalyst 3 revealed that it had uniform mesopores of about 6.3 nm (see Supplementary Information in Figure S3), which were similar to that of the corresponding pure Me@HS@MSN and HS@PPh2@MSN materials, except for the reduced surface area (64.72 m 2 /g for HS@PPh2@MSN, 51.23 m 2 /g for catalyst 3, versus 74.72 m 2 /g for Me@HS@MSN), and pore volume (0.14 cm 3 /g for HS@PPh2@MSN, 0.08 cm3/g for catalyst 3, versus 0.17 cm 3 /g for Me@HS@MSN) suggesting that the decoration of the PPh2 and the complexation of Pd with PPh2 led to nanopore narrowing in catalyst 3. Figure 5 presented the hollow-shell-structured morphology of catalyst 3. Its SEM images showed that the nanospheres were uniformly dispersed; its average particle size was ~445 nm (Figure 5a). The TEM images were also collected and showed that each nanosphere had a cavity of The morphology and ordered mesostructure of three were further investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption-desorption measurements. As shown in Figure 4, the nitrogen adsorptiondesorption isotherm of three showed a typical type IV isotherm with an H 1 hysteresis loop and a visible step at P/P 0 = 0.45-0.95 demonstrating its mesoporous structure. The pore size distribution of catalyst 3 revealed that it had uniform mesopores of about 6.3 nm (see Supplementary Information in Figure S3), which were similar to that of the corresponding pure Me@HS@MSN and HS@PPh 2 @MSN materials, except for the reduced surface area (64.72 m 2 /g for HS@PPh 2 @MSN, 51.23 m 2 /g for catalyst 3, versus 74.72 m 2 /g for Me@HS@MSN), and pore volume (0.14 cm 3 /g for HS@PPh 2 @MSN, 0.08 cm 3 /g for catalyst 3, versus 0.17 cm 3 /g for Me@HS@MSN) suggesting that the decoration of the PPh 2 and the complexation of Pd with PPh 2 led to nanopore narrowing in catalyst 3. Figure 5 presented the hollow-shell-structured morphology of catalyst 3. Its SEM images showed that the nanospheres were uniformly dispersed; its average particle size was~445 nm (Figure 5a). The TEM images were also collected and showed that each nanosphere had a cavity of 369 nm diameter, and the thickness of the silica shell was about 82 nm ( Figure 5b). Further, in the TEM images, under a large-scale bar, we could find that Pd was concentrated on the inner sphere; however, the particle size of Pd was still ambiguous. This might be due to Pd 2+ ions being coordinated with diphenyl(2-(triethoxysilyl)ethyl)phosphane. This phenomenon further confirmed that there were no Pd nanoparticles dispersed in the hollow cavity. Furthermore, a TEM image with chemical mapping was ( Figure 5c) also collected, demonstrating that palladium active centers were successfully entrapped within the inner cavity. on the inner sphere; however, the particle size of Pd was still ambiguous. This might be due to Pd 2+ ions being coordinated with diphenyl(2-(triethoxysilyl)ethyl)phosphane. This phenomenon further confirmed that there were no Pd nanoparticles dispersed in the hollow cavity. Furthermore, a TEM image with chemical mapping was (Figure 5c) also collected, demonstrating that palladium active centers were successfully entrapped within the inner cavity.   on the inner sphere; however, the particle size of Pd was still ambiguous. This might be due to Pd 2+ ions being coordinated with diphenyl(2-(triethoxysilyl)ethyl)phosphane. This phenomenon further confirmed that there were no Pd nanoparticles dispersed in the hollow cavity. Furthermore, a TEM image with chemical mapping was (Figure 5c) also collected, demonstrating that palladium active centers were successfully entrapped within the inner cavity.

Catalytic Performance of the Heterogeneous Catalyst
With the obtained well-established heterogeneous catalyst on hand, a series of Suzuki-Miyaura cross-coupling reactions were optimized, as shown in Table 1. During this process, we chose the Suzuki-Miyaura cross-coupling reaction of 1-iodo-4-methoxyben-

Catalytic Performance of the Heterogeneous Catalyst
With the obtained well-established heterogeneous catalyst on hand, a series of Suzuki-Miyaura cross-coupling reactions were optimized, as shown in Table 1. During this process, we chose the Suzuki-Miyaura cross-coupling reaction of 1-iodo-4-methoxybenzene (4a) and phenylboronic acid (5a) as a model reaction, wherein the reaction was carried out by using 1.0 mol% of Pd-loading in three as a catalyst at 35 • C for the optimization of the reaction conditions. In the case of the screen of bases, we found that the Na 2 CO 3 was the optimal base because the reaction produced the targeted product 4-methoxy-1,1 -biphenyl (6a) in a 95% isolated yield, which was better than those with other bases (Table 1, entry 1 versus entries 2-6). Additionally, a series of co-solvents were screened, and the results showed that the activity of the catalyst 3 for the Suzuki-Miyaura reaction was better in the hydrophilic solvent (Table 1, entries 7-9) than in the hydrophobic solvent (Table 1, entries [10][11][12], and the optimal co-solvent was MeOH/H 2 O (v/v = 2/1). Especially, differing from the traditional high temperature for Suzuki-coupling, the catalysis activity of the catalyst 3 did not increase with increasing temperature ( Table 1, entries [13][14][15][16]. Those findings demonstrated that the Suzuki-Miyaura cross-coupling reaction catalyzed by catalyst 3 with 1 mol% Pd-loading in 3.0 mL of the co-solvent MeOH/H 2 O (v/v = 2/1) at 35 • C gave the best result. It was worth mentioning that the model reaction catalyzed by three had an obviously higher yield than that obtained with the homogenous Pd(OAc) 2 , and even than that with a mixture of Pd(OAc) 2 and PPh 3 ( Table 1, entry 1 versus entries 2-5).

Catalytic Performance of the Heterogeneous Catalyst
With the obtained well-established heterogeneous catalyst on hand, a series of Suzuki-Miyaura cross-coupling reactions were optimized, as shown in Table 1. During this process, we chose the Suzuki-Miyaura cross-coupling reaction of 1-iodo-4-methoxybenzene (4a) and phenylboronic acid (5a) as a model reaction, wherein the reaction was carried out by using 1.0 mol% of Pd-loading in three as a catalyst at 35 °C for the optimization of the reaction conditions. In the case of the screen of bases, we found that the Na2CO3 was the optimal base because the reaction produced the targeted product 4-methoxy-1,1′biphenyl (6a) in a 95% isolated yield, which was better than those with other bases ( Table  1, entry 1 versus entries 2-6). Additionally, a series of co-solvents were screened, and the results showed that the activity of the catalyst 3 for the Suzuki-Miyaura reaction was better in the hydrophilic solvent (Table 1, entries 7-9) than in the hydrophobic solvent ( Table  1, entries 10-12), and the optimal co-solvent was MeOH/H2O (v/v = 2/1). Especially, differing from the traditional high temperature for Suzuki-coupling, the catalysis activity of the catalyst 3 did not increase with increasing temperature ( Table 1, entries [13][14][15][16]. Those findings demonstrated that the Suzuki-Miyaura cross-coupling reaction catalyzed by catalyst 3 with 1 mol% Pd-loading in 3.0 mL of the co-solvent MeOH/H2O (v/v = 2/1) at 35 °C gave the best result. It was worth mentioning that the model reaction catalyzed by three had an obviously higher yield than that obtained with the homogenous Pd(OAc)2, and even than that with a mixture of Pd(OAc)2 and PPh3 ( Table 1, entry 1 versus entries 2-5). To elucidate the benefit of the surface protection of -Si(Me) 3 for the designed silicasupported heterogeneous catalyst 3, the kinetic reaction profiling for the Suzuki-Miyaura cross-coupling reaction catalyzed by Pd(OAc) 2 , three, and 3 (the three capped with-Si(CH 3 ) 3 groups was obtained by silanization of 3 and hexamethyldisilazane) were compared to demonstrate their differences in the catalytic performance ( Figure 6). It was found that three had a higher reaction speed and yield than that attained with the others, elucidating that surface silanols in catalyst 3 could promote synergistically cross-coupling by concentrating reactants inside the hollow shell. This observation was strongly similar to that reported in the literature [52,53], disclosing the superiority of the designed catalyst 3.

Si(Me)3 as a catalyst.
To elucidate the benefit of the surface protection of -Si(Me)3 for the designed silicasupported heterogeneous catalyst 3, the kinetic reaction profiling for the Suzuki-Miyaura cross-coupling reaction catalyzed by Pd(OAc)2, three, and 3′ (the three capped with-Si(CH3)3 groups was obtained by silanization of 3′ and hexamethyldisilazane) were compared to demonstrate their differences in the catalytic performance ( Figure 6). It was found that three had a higher reaction speed and yield than that attained with the others, elucidating that surface silanols in catalyst 3 could promote synergistically cross-coupling by concentrating reactants inside the hollow shell. This observation was strongly similar to that reported in the literature [52,53], disclosing the superiority of the designed catalyst 3. Having established the above catalytic system, the general applicability of the Suzuki-Miyaura cross-coupling reaction was further investigated with a series of substituted aryl boronic acid and aryl halide as substrates ( Table 2). As expected, catalyst 3 could convert various two-component substrates smoothly into the responding biphenyl derivatives in good yields (85-95%), bearing both electron-donating and electron-withdrawing substituents on the meta/para-position except the aryl halide derivatives with nitro on the ortho-position, which got a relatively low yield (85%; Table 2, entry 4), similar to those reported in the literature [38]. Having established the above catalytic system, the general applicability of the Suzuki-Miyaura cross-coupling reaction was further investigated with a series of substituted aryl boronic acid and aryl halide as substrates ( Table 2). As expected, catalyst 3 could convert various two-component substrates smoothly into the responding biphenyl derivatives in good yields (85-95%), bearing both electron-donating and electron-withdrawing substituents on the meta/para-position except the aryl halide derivatives with nitro on the ortho-position, which got a relatively low yield (85%; Table 2, entry 4), similar to those reported in the literature [38].
Beyond the aim of the construction of a site-isolated heterogeneous catalyst 3 for the Suzuki-Miyaura cross-coupling reaction, another important consideration in the design of heterogeneous catalyst was the ease of separation by simple centrifugation and the ability to retain its catalytic activity and enantioselectivity after multiple recycles. It was found that the heterogeneous catalyst 3 could be easily recovered by simple centrifugation. It was found that, in five consecutive reactions, the recycled catalyst 3 could still give 90% ee in the Suzuki-Miyaura cross-coupling reaction of 1-iodo-4-methoxybenzene and phenylboronic acid (see Supplementary Information Figure S10).

Characterization
The Fourier transform infrared (FTIR) spectra were collected by using the KBr method on a Nicolet Magna 550 spectrometer. Nitrogen adsorption isotherms were measured at 77 K with a Quantachrome Nova 4000 analyzer. The samples were measured after being outgassed at 423 K overnight. Pore size distributions were calculated by using the BJH model. The specific surface areas (SBET) of samples were determined from the linear parts of the BET plots (P/P 0 = 0.05-0.3). Solid-state NMR experiments were explored on a Bruker AVANCE spectrometer at a magnetic field strength of 9.4 T with an 1 H frequency of 400.1 MHz, a 13 C frequency of 100.5 MHz, and a 29 Si frequency of 79.4 MHz with 4 mm rotor at two spinning frequencies of 5.5 kHz and 8.0 kHz; TPPM decoupling was applied during the acquisition period. 1 H cross-polarization in all-solid-state NMR experiments was employed using a contact time of 2 ms and the pulse lengths of 4 µs. Scanning electron microscopy (SEM) images were obtained using a JEOL JSM-6380LV microscope operating at 29 kV. Transmission electron microscopy (TEM) images were performed on a JEOL JEM2010 electron microscope at an acceleration voltage of 220 kV.

Preparation of the Catalyst 3
The silicate yolk was synthesized according to the method descibed in the literature. First, dissolving the cetyltrimethylammonium bromide (CTAB, 0.10 g, 0.27 mmol) completely in an aqueous sodium hydroxide (45.0 mL, 0.35 mmol, 2.0 N), and stirring the mixture for 0.5 h at 80 • C. Subsequently, tetraethoxysilane (TEOS, 0.46 mL, 2.07 mmol) was dropped under vigorous stirring at room temperature. Finally, ethyl acetate (0.40 mL) was added, and the mixture was stirred for 2 h at 80 • C. The second step was to coat the above silicate yolk. After cooling down the above reaction mixture to 38 • C, an aqueous solution containing water (80 mL), ethanol (50 mL), CTAB (0.30 g, 0.82 mmol), and NH 3 ·H 2 O (25 wt%, 1.0 mL) was added. The mixture was stirred again at 38 • C for 0.5 h, an additional part of the TEOS (0.5 mL, 2.26 mmol) was added, and the mixture was stirred for another 2 h at 38 • C. Then, 3 mL of a mixture solution containing H 2 O (3.0 mL), CTAB (0.080 g, 0.22 mmol), and NH 3 ·H 2 O (25 wt%, 0.20 mL) was added and stirred at 38 • C for 0.5 h. Finally, 1,2-bis(triethoxysilyl)ethane (0.89 g, 0.70 mmol) were added and the reactant was vigorously stirred for 2.0 h. After filtering and washing with H 2 O and EtOH three times and dried at 60 • C in a vacuum drying oven, the SiO 2 @NPs (about 1 g) were obtained. SiO 2 @NPs (1 g) were added into a 100 mL schlenk tube in an argon atmosphere; then, 25 mL anhydrous toluene containing hexamethyldisiloxane (HMDS, 5.0 mL, 0.025 mmol) was dropped into the schlenk tube, and stirred at room temperature for 24 h. The solid (Me@SiO 2 @NPs) was obtained after filtration and washed with acetone. The third step was the selective etching to remove the surfactant and form the yolk-shell-structured mesoporous nanoparticles. Immersing the collected solids (1.0 g) in an ammonium nitrate (80 mg, 1.0 mmol) solution of ethanol (120 mL, 95%) and stirring the mixture at 60 • C for 12 h left the target hollow-shell structures of Me@HS@MSN (1)

General Procedure for the Suzuki-Miyaura Cross-Coupling
Catalyst 3 (5.0 µmol of Pd based on the ICP analysis, 5.0 mg, 1 mol%), aryl boronic acid (0.75 mmol), aryl halide (0.5 mmol), K 2 CO 3 (1.0 mmol), and 3.0 mL MeOH/H 2 O (v/v = 2/1) co-solvent were added into a 10 mL round-bottom flask; then the mixture was allowed to react for 1-3 h at 35 • C. The reaction was monitored by TLC (thin layer chromatography) to determine the completion of the reaction. Then the catalyst was separated by centrifugation (10,000 rpm) for the recycling experiment, while the aqueous solution was extracted by Et 2 O (3 × 3.0 mL). Further, the combined organic phase was washed by brine and dehydrated with Na 2 SO 4 . After the concentration, the desired product was purified by column chromatography.

Conclusions
In conclusion, a palladium diphenylphosphine-based hollow-shell-structured mesoporous silica heterogeneous catalyst 3 was prepared. The structure of catalyst 3 was analyzed by 13 C CP/MAS NMR, BET, FTIR, ICP, XPS, and electron microscopy. As presented in this study, catalyst 3 realized an efficient Suzuki-Miyaura cross-coupling of 1-iodo-4-methoxybenzene and phenylboronic acid to afford a range of biaryls with up to 95% yield; the activity was comparable to those of related homogeneous and other core/hollow shell solid catalysts. Additionally, catalyst 3 could be recovered after filtering and washing and maintained its high activity in four consecutive reactions in Suzuki-Miyaura coupling. This work offered a perspective approach to design heterogeneous catalysts for high catalytic activity and cost-effective catalysis.