Physico-chemical properties and catalytic activity of the sol-gel prepared Ce-ion doped LaMnO3 perovskites

Anees A Ansari,Abdulrahman A Alwarthan,Abdulrahman Albadri,Ashfaq Ahmad,Basel F Alrayes,Abdullah M Al-Enizi,Naushad Ahmad,Shahid M Ramay,Syed F Adil,Mohamed E Assal,Manawwer Alam

doi:10.1038/s41598-019-44118-1

Anees A Ansari, Abdulrahman A Alwarthan + Show 9 more

Open Access

https://doi.org/10.1038/s41598-019-44118-1

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Abstract

Ce-doped LaMnO3 perovskite ceramics (La1−xCexMnO3) were synthesized by sol-gel based co-precipitation method and tested for the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 25–42% was achieved with benzaldehyde as the main product. X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H2-TPR), temperature-programmed oxidation (O2-TPO), FT-IR and UV-vis spectroscopic techniques were used to examine the physiochemical properties. XRD analysis demonstrates the single phase crystalline high purity of the perovskite. The Ce-doped LaMnO3 perovskite demonstrated reducibility at low-temperature and higher mobility of surface O2-ion than their respective un-doped perovskite. The substitution of Ce3+ ion into the perovskite matrix improve the surface redox properties, which strongly influenced the catalytic activity of the material. The LaMnO3 perovskite exhibited considerable activity to benzyl alcohol oxidation but suffered a slow deactivation with time-on-stream. Nevertheless, the insertion of the A site metal cation with a trivalent Ce3+ metal cation led to an enhanced in catalytic performance because of atomic-scale interactions between the A and B active site. La0.95Ce0.05MnO3 catalyst demonstrated the excellent catalytic activity with a selectivity of 99% at 120 °C.

Highlights

(H2-temperature program reduction (TPR)), temperature-programmed oxidation (O2-temperature program oxidation (TPO)), FT-IR and UV-vis spectroscopic techniques were used to examine the physiochemical properties
For characterization various techniques were applied including X-ray diffraction pattern (XRD), transmission electron microscope (TEM), energy dispersive x-ray analysis (EDX), N2 adsorption, Fourier transform infrared (FTIR), optical absorption (UV-Vis), thermogravimetric analysis (TGA), temperature program reduction (TPR), temperature program oxidation (TPO) and X-ray photoelectron spectroscopy (XPS) techniques
Any other diffraction line associated with MnO or CeO2 is not identified over the whole XRD range specifies the homogeneous dispersion into the crystal lattice and formation of perfect single phase LaMnO3 perovskite

Summary

Results and Discussion

The distinct diffraction lines of perovskite in XRD pattern can be assigned to the (012), (110), (104), (202), (024), (122), (116), (214), (018), (208) and (128) lattice planes, which are attributed to the hexagonal structure of LaMnO3 nanoparticles(Fig. 1) (JCPDS card No 032-0484)[6,19]. On substituted of small radius Ce3+ (1.25 Å) in place of La(1.27 Å), the reflection lines slightly shifted to higher 2θ, signifying that the crystal arrangement becomes distorted[13,21], resulting the transformation is occurring in the symmetry of crystallographic structure[7,10,22]. The structural parameters after calcination of Ce substituted LaMnO3 catalysts, Specific surface area (BET), pore volume (PV) and average pore size (PD) are summarized in Figure 2. (a) TEM image and (b) EDX analysis of LaMnO3, nanoparticles

Single point Multi point Pore volume Pore size

Conclusions

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