Tuning the Selectivity of Catalytic Nitrile Hydrogenation with Phase-Controlled Co Nanoparticles Prepared by Hydrosilane-Assisted Method

Cobalt (Co) is a promising candidate to replace noble metals in the hydrogenation process, which is widely employed in the chemical industry. Although the catalytic performance for this reaction has been considered to be significantly dependent on the Co crystal phase, no satisfactory systematic studies have been conducted, because it is difficult to synthesize metal nanoparticles that have different crystalline structures with similar sizes. Here we report a new method for the synthesis of cobalt nanoparticles using hydrosilane as a reducing agent (hydrosilane-assisted method). This new method uses 1,3-butanediol and propylene glycol to successfully prepare fcc and hcp cobalt nanoparticles, respectively. These two types of Co nanoparticles have similar sizes and surface areas. The hcp Co nanoparticles exhibit higher catalytic performance than fcc nanoparticles for the hydrogenation of benzonitrile under mild conditions. The present hcp Co catalyst is also effective for highly selective benzyl amine production from benzonitrile without ammonia addition, whereas many catalytic systems require ammonia addition for selective benzyl amine production. Mechanistic studies revealed that the fast formation of the primary amine and the prevention of condensation and secondary amine hydrogenation promote selective benzonitrile hydrogenation for benzylamine over hcp Co nanoparticles.

Cobalt powder (commercial-Co-fcc) was purchased from io-li-tec nanomaterials for comparing the catalytic performance.The oxidation states of Co were found to be highly similar between Si-Co-hcp and Si-Co-fcc nanoparticles.

Supplementary tables and figures
In the Co 2p region of Si-Co-fcc, the peak at 778.2 eV was ascribed to metallic cobalt, while the peak at approximately 779.8 eV indicated cobalt in the +2/+3 oxidation states. 1,2Similarly, for Si-Co-hcp, the peak at 778.3 eV was assigned to metallic cobalt, with the peak around 779.4 eV representing cobalt in the +3 oxidation state. 1,3         The benzylamine (3a) exhibits only one desorption peak, whereas the N-benzylidenebenzylamine (4a) displays two desorption peaks: one at lower temperature, and another at higher temperature.Desorption energy (  ) is calculated using the Redhead equation 6 : Where:   (K) is temperature at the desorption peak maximum.
Since adsorption and desorption are inverse processes, the adsorption energy   is calculated as: To express the adsorption energy of benzylamine (3a) over Reduced-Co-hcp, we use  _3_ℎ .Similarly, Calculated adsorption energies: In conclusion, there is no significant difference in adsorption energy of 3a and 4a between Reduced-Co-hcp and fcc.The calculation formula of the specific surface area:  means the density of cobalt, 8.9/ 3 .a Reaction conditions: catalyst (20 mg), 1a (0.5 mmol), toluene (5 mL), pH2 (0.5 MPa), 2.5 h.

Sample
b Determined by GC.

N-benzylidenebenzylamine reduced ratio (%) a
Reduced-Co-hcp 1 0 Reduced-Co-fcc 12  26   a The reduced ratio is determined by subtracting the initially added amount of the organic compound from the quantity adsorbed, as measured by GC, after the completion of a 1-hour period.
The chlorobenzene adsorption was carried out using the same process, excluding the addition of Ncontaining organic compounds, for a duration of 1 hour, with toluene serving as the internal standard.
Consequently, the adsorption quantities of chlorobenzene over reduced-Co-hcp and reduced-Co-fcc nanoparticles were comparable, and the reduced ratios of chlorobenzene were both 1%.

Figure S3 .
Figure S3.XRD patterns of the Si-Co-fcc preparation controlled by Co source with 3 mmol phenylsilane and 5 mL 1,3-butanediol under 200 °C and Air.

Figure S7 .
Figure S7.XRD patterns of Si-Co-hcp nanoparticles treated by 5 M and 2 M NaOH in methanol solution after 5 h at room temperature.

Figure S12 .
Figure S12.The yield of primary amine in the reductive amination process of benzyldehyde on reduced-Co-hcp or reduced-Co-fcc was investigated under the following conditions: 5 mmol of benzyldehyde, 20 mg of catalyst, 5 mL of toluene, 70 °C, 0.5 MPa of H2 and 0.4 MPa NH3.

Figure S13 .
Figure S13.N-benzylidenemethanamine hydrogenation in the presence of benzylamine without H2 on (a) reduced-Co-hcp and (b) reduced-Co-fcc (c) no catalyst was investigated under the following conditions: 5 mmol of N-benzylidenemethanamine, 5 mmol of benzylamine, 20 mg of catalyst, 5 mL of toluene, 70 °C.
the adsorption energies of 3a on Reduced-Co-fcc and 4a on Reduced-Co-hcp and Reduced-Co-fcc for the left peaks (1) and right peaks (2) in Figure SE.

8 .
9/ 3 ×    means the specific surface area of one cobalt atom. 1 means the surface area of one cobalt atom. 1 means the weight of one cobalt atom. 1 means the volume of one cobalt atom. means the diameter of one cobalt atom.Diameter is derived by the Scherrer equation from XRD measurements.

Table S1 .
Reaction conditions for synthesis of fcc and hcp NPs. a

Table S2 .
Atomic concentration of Co 2p to Si 2s in Si-Co-fcc and Si-Co-hcp.

Table S3 .
The surface and structure parameters of hydrosliane-assisted method synthesized Si-Co-hcp and Si-Co-fcc nanoparticles, the base treated Co nanoparticles and the commercial Co-fcc nanoparticles, and the cobalt nanoparticles in the reported literatures.
a derived by the Scherrer equation from XRD measurements.b assuming Co nanoparticles are spherical particles.

Table S4 .
The atomic concentration of Si and Co element in Si-Co-hcp, Si-Co-fcc, reduced-Co-hcp and reduced-Co-fcc through STEM-EDS analysis.

Table S6 .
Comparison of primary amine selectivity with literature reports in nitrile hydrogenation over Co catalyst.