Efficient Alkyne Semihydrogenation Catalysis Enabled by Synergistic Chemical and Thermal Modifications of a PdIn MOF

Recently, there has been a growing interest in using MOF templating to synthesize heterogeneous catalysts based on metal nanoparticles on carbonaceous supports. Unlike the common approach of direct pyrolysis of PdIn-MOFs at high temperatures, this work proposes a reductive chemical treatment under mild conditions before pyrolysis (resulting in PdIn-QT). The resulting material (PdIn-QT) underwent comprehensive characterization via state-of-the-art aberration-corrected electron microscopy, N2 physisorption, X-ray absorption spectroscopy, Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. These analyses have proven the existence of PdIn bimetallic nanoparticles supported on N-doped carbon. In situ DRIFT spectroscopy reveals the advantageous role of indium (In) in regulating Pd activity in alkyne semihydrogenation. Notably, incorporating a soft nucleation step before pyrolysis enhances surface area, porosity, and nitrogen content compared to direct MOF pyrolysis. The optimized material exhibits outstanding catalytic performance with 96% phenylacetylene conversion and 96% selectivity to phenylethylene in the fifth cycle under mild conditions (5 mmol phenylacetylene, 7 mg cat, 5 mL EtOH, R.T., 1 H2 bar).


S1. Materials and General methods
Materials: All reagents and solvents used here were of high purity grade and purchased from Merck company.
Only, 4-ethynylaniline, 1-chloro-4-ethynylbenzene and 1-chloro-3-ethynylbenzene were purchased from TCI company.Pd-based metal-ligand was prepared by the ligand exchange process. 1 mmol of bis(benzonitrile)palladium(II) chloride (C 6 H 5 CN) 2 PdCl 2 and 2 mmol of pyridine-3,5-dicarboxylic acid were dissolved in 150 mL dry THF under inert atmosphere (Ar).Then, the mixture was stirred for 5 h at room temperature to yield a yellow solution.Then, the resulting mixture was concentrated, and the final product was precipitated using 250 mL of hexane.The product was collected by vacuum filtration, washed with THF/hexane and hexane and finally vacuum dried.The purity of the resulting metal complex has been checked by NMR 1 H in CD 3 OD (Figure S1). ) at 800 °C for 2 h (ramp 25 °C•min -1 ).Then, the material was cooled down to room temperature under a higher N 2 flow (40 mL•min -1 ).S2.1.3.Preparation of H 4 L-Q H 4 L (400 mg) were placed into a 300 mL hydrogenation reactor with a solution of 80 mmol of nitrobenzene and 80 mL of toluene (yellow mixture).The system was sealed and pressurized at 5 H 2 bar at room temperature.

S2. Synthesis and characterization
After 24 h of vigorous magnetic stirring, the resulting dark solution was filtrated under vacuum to recover the material.Then, the material was washed several times with methanol and activated at 300 °C under vacuum for 6 h.

S2.1.4. Preparation and characterization of H 4 L-QT
In order to synthesize H 4 L-QT, a pyrolytic thermal treatment was applied to the previously depicted material (H 4 L-Q).Accordingly, 200 mg of PdIn-Q (before the activation step) were pyrolyzed in a tubular fixed-bed reactor under N 2 flow (20 mL•min -1 ) at 800 °C for 2h (ramp 25 °C•min -1 ).Then, the material was cooled down to room temperature with a higher N 2 flow (40 mL•min -1 ).

PdIn-MOF
See Main Text (Experimental Section) for detailed synthesis procedure.

Figure S1. 1 H
Figure S1. 1 H NMR spectra of synthesized Pd complex

Figure S2 .
Figure S2.PdIn-MOF characterization.(a) SEM picture showing nanocrystals and the corresponding EDS analysis of Pd, In, C, N and O elements.(b) PXRD after immersion in different solutions during 24h (c) Black: Thermogravimetric analysis (TGA) using a heating rate of 25 ⁰C•min -1 under air flow.Mustard: The derivative of weight loss with temperature.(d) CO 2 gas adsorption isotherm measured at 273K.

Figure S5 . 2 PdFigure
Figure S5.Total Free Energy Evolution during the reaction nPd + mIn  Pd n In m considering an availability of reactants corresponding to a Pd/In molar ratio value of 1.The whole range of Pd-In stoichiometries are considered.

Figure S7 .
Figure S7.Results of the STEM-EDX and STEM-EELS of PdIn-Q sample a) HAADF image and the corresponding chemical maps Pd b) and In c),and d) a representative EDS spectra.STEM-EELS study including a HAADF image e) and the images corresponding to the three components of the ICA analysis of the whole set of STEM-EELS-SI data f), g) and h).EELS spectra corresponding to the three independent components i).

Figure S8 .
Figure S8.HRTEM image with zoom of carbon coated nanoparticle of PdIn-QT material.Both C-N-O and C-O layers are detected.

Figure S12 .
Figure S12.Curve-fittings and |FT| of the k 3 -weighted χ(k) functions of PdIn-MOF and PdIn-Q at Pd and In K-edges.Coloured circles refer to experimental data while solid lines represent the fits.

Figure S13 .
Figure S13.Curve-fittings and |FT| of the k 3 -weighted χ(k) functions of PdIn-T and PdIn-QT at Pd and In Kedges.Coloured circles refer to experimental data while solid lines represent the fits.
Figure S14.a), b) Kinetic curves and hot filtration of PdIn-Q, PdIn-QT catalyst and c) Kinetic curve of PdIn-T catalyst.d) Alkene and alkyne conversion with PdIn-QT catalyst during an experiment with a mix of substrate (9:1 eq respectively) e) comparison of PdIn-QT activity between phenylacetylene hydrogenation and styrene hydrogenation independently.f) Activity and selectivity of PdIn-QT catalyst at different temperature (24°C, 40°C and 60°C).

Figure S16 .
Figure S16.a) Kinetic curves of Pd@C commercial, b) Kinetic curve comparison of Pd@C commercial activity between phenylacetylene hydrogenation and styrene hydrogenation independently and c) Alkene and alkyne conversion with Pd@C commercial catalyst during an experiment with a mix of substrate (9:1 eq respectively).

Figure S18 .
Figure S18.Conversion and Selectivity kinetic curves of PdIn-QT catalyst in selective hydrogenation of various alkyne compounds.

Figure S19 .
Figure S19.Conversion and Selectivity kinetic curves of PdIn-QT catalyst in each cycles of the stability study.

Figure S20 .
Figure S20.STEM-EDX and STEM-EELS of PdIn-QT after 5 catalytic cycles a) HAADF image and the corresponding chemical maps extracted from the STEM-SI-EDS Pd b) and In c).STEM-EELS study including a HAADF image d) and the images corresponding to the two components of the ICA analysis of the whole set of STEM-EELS-SI data e) and f).EELS spectra corresponding to the two independent components g), a Pd-In component and a C-N-O component.

Table S1 . ICP and EA results for PdIn-MOF sample. Material Pd wt% a In wt% a N wt% b C wt% b H wt% b
a From ICP. b From EA.

Table S3 .
Summary of EXAFS fits of PdIn-MOF and PdIn-Q samples.

Table S4 .
State of the art of Pd-based monometallic and bimetallic catalysts in selective hydrogenation of phenylacetylene under analogous reaction conditions to those used in this work.Aimed at establishing a meaningful consideration and due to the lack of complete kinetic data, TON, TOF and productivity values were all calculated at the highest level of conversion and selectivity reported for each catalyst under consideration. Note: