Monometallic Cerium Layered Double Hydroxide Supported Pd-Ni Nanoparticles as High Performance Catalysts for Lignin Hydrogenolysis

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.

Enhancing the performance of heterogeneous palladium based catalysts in the mild reductive depolymerization of soda lignin through addition of a non-noble metal and tuning of the preparation strategy

“…As a result, the temperature inside of the reactors is 180 °C. All catalysts as well as the experiments without the catalyst (0Cata) and in the presence of pristine g-Al 2 O 3 (Al 2 O 3 ) were studied at reaction times of 3 h (with the exception of Pd-calc and Pd-red, which were tested at 2 h), 6 h and 20 h. However, note that, in order to account for slight deviations in metal contents between the various catalysts, the catalyst performance was assessed as a function of batch time (s (mmol Pd s)), which is dened as the molar amount of Pd added to the reactor (n Pd , mmol Pd) multiplied by the reaction time (Dt, s), and can be calculated from eqn (1), in which m catalyst (g) represents the catalyst mass added to the reactor, wt% Pd is the weight percentage of Pd on the catalyst support as determined through ICP-OES analysis and MM Pd , the molar mass of Pd (g mol −1 ).…”

“…Consequently, the depolymerization of lignin has emerged as a subject of growing research interest. [1][2][3][4][5][6][7][8][9][10] While macropolymer lignin, i.e., extracted from the biomass but not yet depolymerized, is already used for the production of adhesives, emulsiers, plastics and other products, 4,7 selectively depolymerizing said lignin to its functionalized aromatic building blocks would provide sustainable alternatives to fossil based benzene, toluene and xylene (BTX) derivatives, which are crucial platform molecules within the polymer and pharmaceutical industries. [5][6][7][8] A wide range of depolymerization strategies have been developed, which can be categorized as acid catalyzed, base catalyzed, oxidative, reductive, thermal or solvolytic depolymerization.…”

Synthesis of layered double hydroxides: Investigating the impact of stirring conditions and reactor design parameters

“…The studies conducted by Sun et al [ 16 ] already signaled the need to expand the study of reaction conditions by including other parameters, such as agitation rate and reagent addition rate. A literature search on process variables applied to the synthesis of LDHs identified some works that mention agitation rates (rpm) and reagent addition rates (mL/min): 200 rpm [ 17 , 18 ], 400 rpm [ 19 ], 700 rpm [ 20 ], 1200 rpm [ 21 ], 1300 rpm and 7.5 mL/min [ 22 ], 1400 rpm [ 23 ], 1 mL/min [ 24 , 25 ], 60 mL/min [ 26 ] and 4 mL/min [ 27 , 28 ]. However, in these works, the effects of these factors on LDH synthesis were not evaluated.…”

Fast screening of Depolymerized Lignin Samples Through 2D‐Liquid Chromatography Mapping

“…[ 1 , 2 , 3 ] As it is the cheapest and most abundantly available inedible biomass, lignocellulosic biomass is commonly recognized as the most scalable and economically viable bio‐source to produce both bio‐fuels and high value chemicals. [ 3 , 4 , 5 , 6 , 7 , 8 , 9 ] Lignocellulose consists of three highly functional biopolymers, namely cellulose, hemicellulose and lignin. The latter consists of functionalized aromatic building blocks, which are linked through mostly ether (C−O) and, to a lesser extent, carbon‐carbon (C−C) bonds, making it the largest renewable source of aromatics.…”

“…In recent years, chemistry and chemical engineering research has been strongly focusing on replacing fossil resources by sustainable alternatives [1–3] . As it is the cheapest and most abundantly available inedible biomass, lignocellulosic biomass is commonly recognized as the most scalable and economically viable bio‐source to produce both bio‐fuels and high value chemicals [3–9] . Lignocellulose consists of three highly functional biopolymers, namely cellulose, hemicellulose and lignin.…”