TY - JOUR
T1 - Stimulus-Responsive Control of Transition States on Nanohybrid Polymer-Metal Catalysts
AU - Huang, Pengcheng
AU - Baldenhofer, Rick
AU - Martinho, Ricardo P.
AU - Lefferts, Leon
AU - Faria Albanese, Jimmy A.
N1 - Funding Information:
The authors gratefully acknowledge financial support from the China Scholarship Council (No. 201809505005). We are grateful to Rodrigo Fernández-Pacheco from Zaragoza University for the TEM analysis and K. Altena-Schildkamp for the chemical analysis. We acknowledge B. Geerdink for technical support.
Publisher Copyright:
© 2023 The Authors. Published by American Chemical Society.
PY - 2023/5/19
Y1 - 2023/5/19
N2 - In designing effective catalysts, one must consider how to control the accessibility and activity of the active sites. Inspired by nature, we have leveraged the chemistry of thermoresponsive poly(N-isopropylacrylamide) (p-NIPAM) to tailor the extent of solvation of the transition state key surface reaction intermediates during the hydrogenation of nitrobenzene to aniline on Pd/SiO2. Detailed reaction kinetics, catalyst characterization, and NMR diffusion-ordered spectroscopy (DOSY)/nuclear Overhauser effect spectroscopy (NOESY) experiments indicate that nitrobenzene reduction is co-limited by both the formation and the hydrodeoxygenation of phenylhydroxylamine (PHA) to aniline (AN) precursor. Transition-state treatment of the kinetic data revealed that when the temperature is below the lower critical solution temperature (LCST) of p-NIPAM (32 °C), the apparent enthalpy of activation decreases 3-fold. This change was attributed to the drop in the apparent enthalpy of activation when the polymer was in a swollen state. A concomitant reduction in the apparent entropy of activation was obtained at these conditions, indicative of losses in the degree of freedom of the kinetically relevant intermediate (i.e., surface hydrogen). At temperatures above the LCST, it was possible to reverse these effects, leading to similar apparent activation energy as that observed in the Pd/SiO2 catalyst. These results establish the foundational work on the development of materials capable of taming the intrinsic activity of the active site in a fast, reversible manner. We envision that these results will facilitate the development of catalysts that can mimic the homeostatic behavior of enzymes, allowing more stable operation even when complex feedstocks are employed (e.g., biomass conversion and pollution control).
AB - In designing effective catalysts, one must consider how to control the accessibility and activity of the active sites. Inspired by nature, we have leveraged the chemistry of thermoresponsive poly(N-isopropylacrylamide) (p-NIPAM) to tailor the extent of solvation of the transition state key surface reaction intermediates during the hydrogenation of nitrobenzene to aniline on Pd/SiO2. Detailed reaction kinetics, catalyst characterization, and NMR diffusion-ordered spectroscopy (DOSY)/nuclear Overhauser effect spectroscopy (NOESY) experiments indicate that nitrobenzene reduction is co-limited by both the formation and the hydrodeoxygenation of phenylhydroxylamine (PHA) to aniline (AN) precursor. Transition-state treatment of the kinetic data revealed that when the temperature is below the lower critical solution temperature (LCST) of p-NIPAM (32 °C), the apparent enthalpy of activation decreases 3-fold. This change was attributed to the drop in the apparent enthalpy of activation when the polymer was in a swollen state. A concomitant reduction in the apparent entropy of activation was obtained at these conditions, indicative of losses in the degree of freedom of the kinetically relevant intermediate (i.e., surface hydrogen). At temperatures above the LCST, it was possible to reverse these effects, leading to similar apparent activation energy as that observed in the Pd/SiO2 catalyst. These results establish the foundational work on the development of materials capable of taming the intrinsic activity of the active site in a fast, reversible manner. We envision that these results will facilitate the development of catalysts that can mimic the homeostatic behavior of enzymes, allowing more stable operation even when complex feedstocks are employed (e.g., biomass conversion and pollution control).
KW - N-isopropylacrylamide
KW - nitrobenzene hydrogenation mechanism
KW - polymer-coated catalyst
KW - solvation effect
KW - transition states
KW - UT-Hybrid-D
UR - http://www.scopus.com/inward/record.url?scp=85156202740&partnerID=8YFLogxK
U2 - 10.1021/acscatal.3c00276
DO - 10.1021/acscatal.3c00276
M3 - Article
AN - SCOPUS:85156202740
SN - 2155-5435
VL - 13
SP - 6590
EP - 6602
JO - ACS catalysis
JF - ACS catalysis
IS - 10
ER -