Role of Surface Acidity in Formation and Performance of Active Ni Single Sites in Supported Catalysts for Butene Dimerization: A View inside by Operando EPR and In Situ FTIR Spectroscopy

Abstract

A series of supported Ni/SiO2–Al2O3 catalysts with the same Ni content but different ratios of Brønsted and Lewis acid sites resulting from different Al/Si ratios have been prepared by impregnation with Ni­(Cp)2 and analyzed by operando electron paramagnetic resonance (EPR) during dimerization of n-butenes under industrially relevant conditions as well as by in situ Fourier transform infrared (FTIR) spectroscopy of adsorbed pyridine and CO to derive relations between the surface acidic properties, the nature of the Ni sites, and the catalytic performance. While EPR monitored the formation of different Ni+ single sites as well as ferromagnetic Ni clusters, it is silent for Ni2+. To compensate for this lack, FTIR spectroscopy of adsorbed CO was used to analyze the relative number and distribution of Ni single sites in both valence states of +1 and +2. This method was also used to analyze the relative number of Brønsted and Lewis acid sites exposed on the surface. Thus, a comprehensive picture on the formation of different Ni surface sites and their role for catalytic performance could be derived. It was found that Brønsted sites have both a positive and negative effect: (1) they stabilize active Ni single species while Lewis sites do not play a significant role for catalytic performance; (2) they promote undesired branching of C8 products. Thus, optimum catalysts should contain a maximum number of single Ni sites in the immediate vicinity of Brønsted surface sites, while an excess of the latter must be avoided to suppress isomerization.

Rational Design of a High-Durability Pt-Based ORR Catalyst Supported on Mn/N Codoped Carbon Sheets for PEMFCs

“…According to previous research studies, metallic state Pt (0) revealed the highest ORR activity. , Moreover, the binding energy of Pt/(Mn–N)@C at the Pt 4f doublet revealed a negative shift (0.13 eV) compared to Pt/XC-72R due to the electron donation from the (Mn–N)@C substrate to Pt. Compared to Pt/N@C, it also revealed a slight negative shift, indicating that the obtained electronic structure has been changed through the process of loading Pt on (Mn–N)@C. The downward shift of the d-band center resulted in the decrease of the electron return of the Pt 5d orbital, thus boosting the ORR. , …”

“…Compared to Pt/N@C, it also revealed a slight negative shift, indicating that the obtained electronic structure has been changed through the process of loading Pt on (Mn−N)@C. The downward shift of the d-band center resulted in the decrease of the electron return of the Pt 5d orbital, thus boosting the ORR. 51,52 The electrocatalytic performance of different Pt/carbon catalysts and carbon substrates toward ORR was evaluated in 0.1 M HClO 4 using the RDE method. Figure 3a shows the different CV curves of four catalysts.…”

Co-utilization of wastewater sludge and heavy metals for single-atom electrocatalytic reduction of gaseous CO2

“…whose pyrrolic N 4 -metal coordination could exist without any vacancy. 27 , 28 Generally, the N 4 -Ni coordination requires relatively lower energy for ECO 2 RR than N 3 -Ni regardless of pyridinic or pyrrolic N coordination ( Figures 6 K and S24 ). This explains that why protein-based catalyst (N 4 -Ni coordination) presents better ECO 2 RR performance than EPS-based catalyst (mixture of N 4 -Ni and N 3 -Ni coordination).…”

Tuning the Micro-coordination Environment of Al in Dealumination Y Zeolite to Enhance Electron Transfer at the Cu–Mn Oxides Interface for Highly Efficient Catalytic Ozonation of Toluene at Low Temperatures

“…Compared with Mn/Y, the weak acid sites of Mn/DY decreased but the proportion of strong acid increased. It is because some of the aluminum species (Si–O–Al–O–Si) in the Y zeolite framework were leached after dealumination, and these aluminum species often constituted the weak Brønsted acid sites of the zeolite . At the same time, the change in the position of Al species may increase the distance between adjacent Al, which can also lead to the enhancement of acidic sites.…”