Cerium

¹H and ¹³C spectra were recorded by a Bruker
Avance III apparatus (400 and 101 MHz). The samples were prepared
by dissolving ca. 20 mg of a compound in 1 mL of deuterated chloroform
(CDCl₃) or dimethyl sulfoxide (DMSO-d₆). Hydrogen nuclei ¹H were excited using the frequency
of 400 MHz. The data are presented as chemical shifts (δ) in
ppm (in parentheses: multiplicity, integration, coupling constant).
For attenuated total reflectance infrared spectroscopy (ATR-IR), IR
spectra were recorded by using a Vertex 70 Bruker spectrometer equipped
with an ATR attachment with a diamond crystal over frequencies of
600–3500 cm^–1 with a resolution of 5 cm^–1 over 32 scans. IR spectra are presented as a function
of transparency (T) expressed in percent (%) against
the wavenumber (v) expressed in cm^–1. For mass spectrometry, mass spectra were obtained on a Waters ZQ
2000 mass spectrometer. Elemental analysis was performed with an Exeter
analytical CE-440 elemental analyzer. For UV–vis absorption
spectroscopy, absorption spectra of the dilute solutions (10^–4–10^–5 moL/L) and thin films of the compounds
were recorded under ambient conditions with a PerkinElmer Lambda 25
spectrophotometer. For photoluminescence (PL) spectroscopy, fluorescence
spectra of thin films and dilute solutions (10^–4–10^–5 moL/L) of the compounds were recorded
at room temperature with a luminescence spectrometer Edinburgh Instruments
FLS980. PL quantum yields of the solutions and thin films were measured
using an integrating sphere. Phosphorescence spectra were recorded
at 77 K. Differential scanning calorimetry (DSC) measurements were
carried out using a TA Instruments Q2000 thermosystem. The samples
were examined at a heating/cooling rate of 10 °C/min under a
nitrogen atmosphere. Thermogravimetric analysis (TGA) was performed
under a nitrogen atmosphere on a TA Instruments Q50 analyzer. The
heating rate was 20 °C/min. Cyclic voltammetry measurements were
performed by using a glassy carbon working electrode (a disk with
a diameter of 2 mm) in a three-electrode cell of an Autolab-type potentiostat–galvanostat.
The measurements were carried out for the solutions in dry dichloromethane
containing 0.1 M tetrabutylammonium hexafluorophosphate at 25 °C;
the scan rate was 50 mV/s, while the sample concentration was 10^–3 M. The potentials were measured against silver as
a quasi-reference electrode. A platinum wire was used as a counter
electrode. The potentials were calibrated with the standard ferrocene/ferrocenium
(Fc/Fc⁺) redox system.^{20 (link)} Ionization
energy (IE) was calculated by employing the following formula 1:^{21 (link),22 (link)}

A series of cerium manganese catalysts with Ce:Mn atomic ratio of 6:4 were prepared by co-precipitation using Ce(NO₃)₃·6H₂O (AR grade, Yutai Qixin Chemical, China) and Mn(NO₃)₂ (AR grade, Xiya Reagent, China) as starting materials. The precipitants used were NaOH (3 mol·L⁻¹), Na₂CO₃ (3 mol·L⁻¹), (NH₄)₂CO₃ (3 mol·L⁻¹), NH₃·H₂O (3 mol·L⁻¹) and a mixture of (NH₄)₂CO₃ and NH₃·H₂O with molar concentration ratio of 3/3, accordingly, the catalysts prepared were abbreviated as CM-Na, CM-NaC, CM-NC, CM-N and CM-3, respectively. The salt solution and the alkali solution were mixed together under continuous stirring, keeping the pH around 8.5–8.8 during this process.. The precipitate slurry was filtered and washed with water. Then the precipitates were dried at 70 °C for 24 h and calcined at 600 °C for 3 h to obtain the prepared catalyst sample. In addition, the catalysts were divided into two groups according to the presence or absence of Na in the precipitant: Na-containing catalysts (CM-Na and CM-NaC) and Na-free catalysts (CM-NC, CM-N and CM-3).