Insights into the Structure-Activity Relationships in Metal-Organic Frameworks-Supported Nickel Catalysts for Ethylene Hydrogenation

Insights into the Structure-Activity Relationships in Metal-Organic Frameworks-Supported Nickel Catalysts for Ethylene Hydrogenation

Wang, X.; Zhang, X.; Pandharkar, R. U.; Lyu, J.; Ray, D.; Yang, Y.; Kato,S.; Liu, J.; Wasson, M. C.; Islamoglu, T.; Li, Z.; Hupp, J. T.; Cramer, C. J.; Gagliardi, L.; Farha, O. K.
ACS Catal. 2020, 10, 8995 (doi:10.1021/acscatal.0c01844).

Solid supports play an indispensable role in heterogeneous catalysis as they can directly affect the catalytic activity and selectivity of supported catalysts. However, the specific roles of such supports remain to be demystified owing to the difficulties in obtaining precise structural information of supported catalysts. To understand the effects of MOF topology, pore environment and metal identity of node supports on catalytic activity, a Ni catalyst was supported on eight Zr- or Hf-MOFs based on 8-connected nodes, namely M-NU-1200, M-NU-1000, M-NU-1008, and M-NU-1010 (M = Zr or Hf). Single crystal X-ray diffraction (SCXRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS) characterized the catalytic structures. To investigate the support effects on their activities, the Ni-supported MOFs catalyzed ethylene hydrogenation as a model reaction. The results revealed that all Hf-based MOFs supported Ni catalysts exhibited higher catalytic reactivity with TOF (turnover frequency) values at least double those of their isostructural Zr counterparts. Additionally, MOFs with less congested metal anchoring sites, as a result of topology and surrounding pore environment, yielding higher TOFs, suggesting the importance of supports in dictating both the catalyst accessibility and subsequent activity. Computational analysis complemented the experimental observations and provided insights into reaction barrier differences to explain their performance variation. This study demonstrates the essential role of the supports and provides a thought for selecting/designing suitable supports in heterogeneous catalysis.