Abstract
Monometallic cerium layered double hydroxides (Ce-LDH) supports were successfully synthesized by a homogeneous alkalization route driven by hexamethylenetetramine (HMT). The formation of the Ce-LDH was confirmed and its structural and compositional properties studied by XRD, SEM, XPS, iodometric analyses and TGA. HT-XRD, N2-sorption and XRF analyses revealed that by increasing the calcination temperature from 200 to 800 °C, the Ce-LDH material transforms to ceria (CeO2) in four distinct phases, i.e., the loss of intramolecular water, dehydroxylation, removal of nitrate groups and removal of sulfate groups. When loaded with 2.5 wt% palladium (Pd) and 2.5 wt% nickel (Ni) and calcined at 500 °C, the PdNi-Ce-LDH-derived catalysts strongly outperform the PdNi-CeO2 benchmark catalyst in terms of conversion as well as selectivity for the hydrogenolysis of benzyl phenyl ether (BPE), a model compound for the α-O-4 ether linkage in lignin. The PdNi-Ce-LDH catalysts showed full selectivity towards phenol and toluene while the PdNi-CeO2 catalysts showed additional oxidation of toluene to benzoic acid. The highest BPE conversion was observed with the PdNi-Ce-LDH catalyst calcined at 600 °C, which could be related to an optimum in morphological and compositional characteristics of the support.
Highlights
Evolutions towards a circular sustainable economy, including the replacement of fossil resources by renewable alternatives are expected to become increasingly important for, a.o., the abatement of climate change
cerium layered double hydroxides (Ce-Layered double hydroxides (LDHs)) materials synthesized within this work agree well with that of the Ce-LDH as synthesized by
The typical reflections at low 2θ values (10◦ and 17◦ ), for layered structures with an interplanar distance (d-spacing) of 0.838 and 0.419 nm, can be found in both patterns in Figure 3 [38]. These reflections appear in the X-ray diffraction (XRD) pattern of rare earth metal layered double hydroxides (LREHs) with intercalated sulfate anions, synthesized by Liang et al [41]
Summary
Evolutions towards a circular sustainable economy, including the replacement of fossil resources by renewable alternatives are expected to become increasingly important for, a.o., the abatement of climate change. Over the past decade, many biorefinery processes have emerged, which in some cases can replace a part of the petrochemical industry, today they lack competitiveness [1]. Lignocellulosic biomass is mainly composed of three biopolymers, i.e., cellulose, hemicellulose and lignin. Since the emergence of the lignocellulosic based biorefinery concept, research has mainly focused on converting cellulose and hemicellulose into consumables, i.e., fuels, chemicals, polymers, medicines, etc. Most large-scale industrial processes that use plant polysaccharides have burned lignin as a low value fuel to generate the power needed to productively transform the biomass [5,6,7]. As lignin is the largest sustainable aromatic feedstock, it constitutes a worthy resource for materials’ applications or for the production of renewable aromatics
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