Journal
CATALYSTS
Volume 11, Issue 2, Pages -Publisher
MDPI
DOI: 10.3390/catal11020210
Keywords
rubidium (Rb); platinum (Pt); zirconia (ZrO2); low temperature water-gas shift (LT-WGS); alkali promotion; electronic effect; formate; associative mechanism; hydrogen
Categories
Funding
- Undergraduate NSF Research Program
- National Science Foundation [1832388]
- Direct For Education and Human Resources
- Division Of Undergraduate Education [1832388] Funding Source: National Science Foundation
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Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate, and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55-0.93% Rb, where the catalyst maintained high activity and exhibited higher stability compared to the unpromoted catalyst.
Recent studies have shown that appropriate levels of alkali promotion can significantly improve the rate of low-temperature water gas shift (LT-WGS) on a range of catalysts. At sufficient loadings, the alkali metal can weaken the formate C-H bond and promote formate dehydrogenation, which is the proposed rate determining step in the formate associative mechanism. In a continuation of these studies, the effect of Rb promotion on Pt/ZrO2 is examined herein. Pt/ZrO2 catalysts were prepared with several different Rb loadings and characterized using temperature programmed reduction mass spectrometry (TPR-MS), temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), an X-ray absorption near edge spectroscopy (XANES) difference procedure, extended X-ray absorption fine structure spectroscopy (EXAFS) fitting, TPR-EXAFS/XANES, and reactor testing. At loadings of 2.79% Rb or higher, a significant shift was seen in the formate nu(CH) band. The results showed that a Rb loading of 4.65%, significantly improves the rate of formate decomposition in the presence of steam via weakening the formate C-H bond. However, excessive rubidium loading led to the increase in stability of a second intermediate, carbonate and inhibited hydrogen transfer reactions on Pt through surface blocking and accelerated agglomeration during catalyst activation. Optimal catalytic performance was achieved with loadings in the range of 0.55-0.93% Rb, where the catalyst maintained high activity and exhibited higher stability in comparison with the unpromoted catalyst.
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