Improvement of Propylene Epoxidation Caused by Silver Plasmon Excitation by UV-LED Irradiation on a Sodium-Modified Silver Catalyst Supported on Strontium Carbonate

Shigeru Sugiyama,Akihiro Furube,Ikumi Okitsu,Yuki Kato,Yutaro Maki,Wataru Ninomiya,Kazuki Hashimoto,Naohiro Shimoda

doi:10.3390/catal11030398

Shigeru Sugiyama, Akihiro Furube + Show 6 more

Open Access

https://doi.org/10.3390/catal11030398

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Abstract

The effect that UV-LED irradiation exerted on a sodium-modified silver catalyst supported on strontium carbonate (Ag-Na/SrCO3) was examined during an epoxidation of propylene to propylene oxide. Based on our previous study, we used Ag(56)-Na(1)/SrCO3 in this study. The numbers in parentheses refer to the weight percentage of silver and sodium. Although this catalyst system did not contain typical photocatalysts such as titanium oxide or tungsten oxide, UV-LED irradiation of Ag(56)-Na(1)/SrCO3 resulted in an evident improvement in the selectivity and yield of propylene oxide. Such an advantageous effect of UV-LED irradiation could not be discussed based on the bandgap used in photocatalysts and, therefore, we proposed a mechanism based on the plasmon excitation of silver, which could be accomplished using the irradiation wavelength of UV-LED to produce electrons. Since the lifespan of these electrons is expected to be short, it is difficult to place them into direct contact with the gas phase of oxygen. Once the generated electrons move to SrCO3, however, the lifespan is improved, which could allow suitable contact with oxygen in the gas phase to form active oxygen. If the oxygen is active for epoxidation as hydrogen peroxide, this could explain the improvement in activity from UV-LED irradiation.

Highlights

Since propylene oxide is a raw material for polyurethane that is widely used in automobile parts, food additives, cosmetics, etc., more than 10 million tons are produced annually worldwide by the petrochemical industry [1]
The PO yield was unavoidably low for the epoxidation of propylene to PO, we focused on the selectivity and yield of PO with time-on-stream on both catalysts
The capillary column in the FID-GC consisted of Stabilwax (Shimadzu GLC Ltd., Tokyo, Japan, 60 m × Φ 0.25 mm × 0.25 μm) for the detection of acetaldehyde, propylene oxide, propionaldehyde, acetone, acrolein, propane, and propylene at column temperatures of 313 K

Summary

Introduction

Since propylene oxide is a raw material for polyurethane that is widely used in automobile parts, food additives, cosmetics, etc., more than 10 million tons are produced annually worldwide by the petrochemical industry [1]. It was evident that the SrCO3 support alone (catalyst (A)) showed no activity for the epoxidation of propylene under UV-LED irradiation conditions. With the loading of silver on SrCO3 (catalyst (B)), the conversion of propylene was enhanced but, again, the effect of UV-LED irradiation was negligible. The effect of UV-LED irradiation on the epoxidation of propylene to PO observed in the present study appeared to be dependent on the interactions of each of the components of the Ag(56)-Na(1)/SrCO3 catalyst. The characterization results shown above were somewhat of an analogue to the normal catalytic reaction regardless of the employment of the thermal- and photo-reactions when using solid catalysts These results could not explain the advantageous effect that UV-LED irradiation exerted on Ag-Na/SrCO3 during the epoxidation of propylene to PO. DFaigsuhreed7l.iKneu:bwelkaav–eMleunngkthfu(n3c6ti5onnsmo)f SdruCeOt3o(bUluVe-LlinEeD) .and Ag(56)-Na(1)/SrCO3 (red line) obtained from the corresponding absorption spectroscopy

Catalyst Preparation

Characterization of the Catalyst

Evaluation of the Catalytic Performance

Conclusions