Creation of Highly Reducible CuO Species by High-Temperature Calcination of a Cu-Al Layered Double Hydroxide: Selective Hydrogenation of Furfural into Furfuryl Alcohol with Formic Acid

Abstract

Highly reducible CuO species were created by the calcination of a Cu-Al layered double hydroxide (CuAl LDH) at 1073 K under air. After this heat treatment, the original layered double hydroxide structure was completely transformed into CuO and CuAl2O4 phases. The synthesized calcined CuAl LDH (calc-CuAl LDH) promoted the catalytic hydrogenation of furfural (FALD) into furfuryl alcohol (FOL) with formic acid (FA) as a hydrogen donor. In the initial stage of the above catalytic reaction, the CuO species in the calc-CuAl LDH matrix transformed into active Cu0 species via the formation of a Cu(HCOO)2-1,4-dioxane complex in the liquid phase. The spent catalyst was also reusable without loss of its high catalytic performance.

Creation of a Highly Active Small Cu‐Based Catalyst Derived from Copper Aluminium Layered Double Hydroxide Supported on α‐Al2O3 for Acceptorless Alcohol Dehydrogenation

“…It is well known that the calcination of LDH composed of Cu 2+ and Al 3+ at high temperatures up to 1023 K leads to the formation of a CuO and stable spinel CuAl 2 O 4 phase [11] . After calcination of the unsupported CuAl LDH at 1073 K, the powder morphology of CuAlO, which contains CuO and CuAl 2 O 4 , [9,10] appeared similar (Figure 1(c)). Well‐dispersed brucite‐like LDH is visible in the image of 12_CuAl LDH@α‐Al 2 O 3 .…”

“…It clearly suggests a considerable amount of original CuAl LDH species remained after calcination at 1073 K. Notably, the layered structure of the CuAl LDH phase on the α-Al 2 O 3 surface was not detected in the XRD profile after calcination at 1073 K. In the case of unsupported CuAl LDH, a composition of 54.5 % CuO and 45.5 % CuAl 2 O 4 , with no CuAl LDH remained, was confirmed by LCF after calcination at 1073 K (Figure S4). [10] The treatment of the CuAlO and CuAlO@α-Al 2 O 3 samples for XANES measurement was the same, so it can be concluded that partial rehydration of metal oxide does not occur. It might be said that the Cu 2 + -Al 3 + mixed hydroxide sheets in the matrix of 12_CuAl LDH@α-Al 2 O 3 are more stable under heat treatment than those of the original CuAl LDH.…”

“…The copper-aluminum layered double hydroxide supported on α-Al 2 O 3 (CuAl LDH@α-Al 2 O 3 ) was prepared using direct coprecipitation of Cu and Al metal salts solution on the α-Al 2 O 3 under alkaline conditions according to the previous report with some modification. [9,10] In the case of 12_CuAl LDH@α-Al 2 O 3 synthesis, the mixture of CuÀ Al metals salt solution was formulated by dissolving Cu(NO 3 ) 2 • 3H 2 O (2.416 g, 10 mmol) and Al(NO 3 ) 3 • 9H 2 O (3.751 g, 10 mmol) into distilled water (50 mL). This mixture solution was added dropwisely using the peristaltic pump into a mixture of aqueous Na 2 CO 3 solution (88.9 mM, 75 mL) and α-Al 2 O 3 (3 g) under vigorous stirring at room temperature.…”

“…It was found that CuO species in the catalyst matrix was easily reduced into Cu 0 during the catalytic reaction even in the low loading amount of Cu. [11] After calcination of the unsupported CuAl LDH at 1073 K, the powder morphology of CuAlO, which contains CuO and CuAl 2 O 4 , [9,10] appeared similar (Figure 1(c)). Well-dispersed brucite-like LDH is visible in the image of 12_ CuAl LDH@α-Al 2 O 3 .…”

Development of Cobalt Oxide Nanocomposite Catalyst from Cobalt Aluminum Layered Double Hydroxide Precursor Towards Aerobic Alcohol Oxidation

“…Mitran et al 5) synthesized a highly efficient Co-Mg-Al mixed oxide derived LDH with welldispersed cobalt species for oxidative dehydrogenation of propane. Another report shows that a highly reducible CuO could be designed by simple calcination of Cu-Al LDH at 1073 K, which then acted as a highly active catalyst towards selective hydrogenation of furfural 13) .…”