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Zirconium tetramandelate (2-hydroxy-2-phenylacetate) has been used for selective gravimetric analysis of zirconium for over 70 years. Herein its crystal structure is reported from synchrotron powder X-ray diffraction and 13C solid-state NMR. The complex is a rare example of isolated zirconium cations, rather than the clusters prevalent in aqueous solutions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Pd-promoted Mn-Ce-Zr and Mn-Pr-Zr mixed oxides showed remarkably high NOx storage efficiency in the range 80–160 °C. • NOx storage efficiency was found to improve with increasing Mn content for 1%Pd/Mn-Ce-Zr materials. • DRIFTS measurements showed that relative to Ce-Zr mixed oxides, Mn incorporation favored NOx storage as nitrate. • NOx stored on Pd/Mn-Ce(Pr)-Zr mixed oxides desorbed at lower temperatures than for Ce-Zr mixed oxides. Abstract Pd-promoted ternary oxides of the type Mn-Ce-Zr and Mn-Pr-Zr were characterized and evaluated for low temperature NOx storage applications such as diesel vehicle cold starts. While X-ray diffraction data were in all cases consistent with the formation of solid solutions, Mn/Zr and Mn/Ce(Pr) ratios found by XPS were consistently higher than the bulk values, indicative of an enrichment of Mn at the surface of the solids. Both sets of Pd-promoted mixed oxides showed remarkably high NOx storage efficiency in the range 80–160 °C, while a 1.8% Pd/Mn(27)-Ce(7)-Zr catalyst showed excellent NOx storage in simulated cold start experiments. Moreover, ramping the temperature to 370 °C in these experiments, simulating higher speed operation, resulted in near complete purging of stored NOx from the catalyst. NOx storage efficiency in isothermal storage experiments was found to improve with increasing Mn content for the 1%Pd/Mn(x)-Ce(7)-Zr series (x = 9, 18, 27 wt.%), DRIFTS measurements showing that relative to Ce-Zr mixed oxides, Mn incorporation favored NOx storage as nitrate. During temperature programmed desorption (TPD) two main desorption events were observed, corresponding to decomposition of nitrites (up to 200 °C), followed by loss of nitrates (⁓200–400 °C). Nitrates stored on Pd/Mn-Ce(Pr)-Zr mixed oxides desorbed during TPD at lower temperatures than for CeO 2 -ZrO 2 mixed oxides, a finding attributed to the lower basicity of Mn compared to Ce. Hydrothermal aging of 1.8%Pd/Mn(27)-Ce(7)-Zr at 700 °C reduced NOx storage efficiency, although the catalyst was still able to store significant amounts of NOx. However, catalyst sulfation led to a large decrease in NOx storage efficiency and the efficiency could not be completely recovered with lean or rich desulfations at high temperatures. [ABSTRACT FROM AUTHOR]