Formation and stability of an active PdZn nanoparticle catalyst on a hydrotalcite-based support for ethanol dehydrogenation

Abstract

A hydrotalcite-based PdZn nanoparticle catalyst, PdZn/MgIJAl)IJPd)IJZn)O x has been synthesized via a onepot procedure. The activation comprising H 2 and air treatmentIJs) allows tuning the nanoparticle formation and, hence, the catalyst performance. Based on an elaborate set of characterization data from EXAFS, in situ XRD, STEM and CO chemisorption, it is concluded that single reduction leads to the formation of Pdrich alloy nanoparticles, i.e., a PdZn shell with a Pd core. Cycled reduction, i.e., 3 subsequent hydrogen and air treatments, ensures the formation of more homogeneously mixed PdZn nanoparticles. Compared with a PdZn/ZnO reference catalyst, the nanoparticles obtained after cycled reduction exhibit a higher initial average turnover frequency in ethanol dehydrogenation, i.e., 7.0 molEtOH (mol Pd s) −1 rather than 3.2 molEtOH (mol Pd s). An activity loss is observed during the first hours on stream. It is attributed to coking of the Pd sites which are also deemed responsible for acetaldehyde decomposition. Hence, the acetaldehyde selectivity steadily increases during the first hours on stream. Subsequently, the acetaldehyde space time yield and selectivity stabilize at 0.7 × 10 −4 mol s −1 kg −1Pd and 98%, respectively.

Ethanol Dehydrogenation: A Reaction Path Study by Means of Temporal Analysis of Products

“…An important topic with respect to catalysts for ethanol dehydrogenation is the significant deactivation that occurs due to coke formation on the catalyst surface and the sintering of the active catalyst particles. This was found in the case of PdZn nanoparticles [28], monometallic Cu [29,30], bi-or tri-metallic Cu alloys [29,[31][32][33], SiO 2 − supported Cu catalysts [34] and V/Mg − Al catalysts [35,36]. There is a considerable number of papers that use computational methods such as density functional theory or a combination of experimental methods and modelling tools to investigate correlations between catalyst activity and selectivity on the one hand and material characteristics such as crystal faces, monolayer coverages, etc., on the other [37][38][39][40][41].…”

Synergistic Effect of Zn in a Bimetallic PdZn Catalyst: Elucidating the Role of Undercoordinated Sites in the Hydrodeoxygenation Reactions of Biorenewable Platforms

“…35 Similarly, upon reduction, formation of a PdZn alloy was observed in a PdZn catalyst supported on hydrotalcite. 36 Upon H 2 treatment at 823 K, hydrogen spillover on Pd particles was attributed to facilitate the reduction of ZnO to Zn, resulting in the formation of an intermetallic PdZn compound. 36 Apart from this, Zn alloyed with Cu is a known industrial catalyst (Cu/ ZnO/Al 2 O 3 ) for methanol synthesis from syngas, 37 where Zn was observed to be reduced to the metallic state to form a CuZn surface alloy.…”

Fingerprint Feature of Atomic Intermixing in Supported AuPd Nanocatalysts Probed by X-ray Absorption Fine Structure

“…Due to the unique catalytic, electronic, and magnetic properties, supported bimetallic nanoparticles (NPs) have attracted extensive attention and been widely used in various important fields for many years, especially in some industrially important catalytic reactions such as hydrogenations, , dehydrogenations, , selective oxidation, , and reactions in fuel cells. − For many catalytic systems, bimetallic catalysts have been demonstrated to possess synergetic catalytic capability which is often superior to their monometallic counterparts. The superior performance of bimetallic nanomaterials is associated with the material morphology (size, shape, etc.…”

“…So it is eagerly desirable for many applications to seek rational routes to develop heterogeneous supported nanocatalysts. For industrial applications, conventional synthetic procedures of supported NP catalysts typically involve the deposition of metal precursors onto supports with high surface area, followed by various thermal activation steps. ,,− Inevitably, the size distribution of NPs and the degree of dispersion on the supports are influenced by many factors, such as pH value, concentration of the precursor solution, type of supports, and especially the calcination temperature and procedure. − ,, Consequently, bimetallic materials prepared by such methods with less controllability for the size and structures of bimetallic NPs are often complicated, leading to significant nonuniformity (chemistry, structure, or particle size/shape).…”

“…1,8,12−15 Inevitably, the size distribution of NPs and the degree of dispersion on the supports are influenced by many factors, such as pH value, concentration of the precursor solution, type of supports, and especially the calcination temperature and procedure. [1][2][3]6,10 Consequently, bimetallic materials prepared by such methods with less controllability for the size and structures of bimetallic NPs are often complicated, leading to significant nonuniformity (chemistry, structure, or particle size/shape). In order to address the above issues and to gain a further understanding for the structure−property relations of bimetallic catalysts, there are two crucial sides which should be solved.…”