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Effect of Shell Pore Microstructure of the Pd Hollow Catalysts Pd@ HMAN for ­H2O2 Generation Dan Guo1,3 · Jiesong Zhang2 · Shen Xiao2 · Lianjun Shi1,2 · Qian Lin2 · Hongyan Pan1,2,3 Received: 4 February 2020 / Accepted: 3 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract  Pd-based hollow catalysts, Pd@HMAN, in which Pd was used as core and hollow aluminosilicate (HMAN) as shell, have been successfully synthesized by self-assembling method. Pd@HMAN-M (M = 1, 1.5, 2, 2.5) with uniform Pd nanoparticle size (~ 9.3 nm) and different shell volume (0.06–0.18 c­ m3g−1) were prepared by varying the addition amount of tetraethyl orthosilicate (TEOS). It is found that the shell pore size of 1–3.5 nm of the catalysts Pd@HMAN-M was conducive to the mass transfer of ­H2, ­O2 and ­H2O2, and the larger the shell pore volume of Pd@HMAN-M was, the larger the adsorption amount of reactant ­H2 was, and thus the higher selective and productive of ­H2O2 could be obtained. The catalyst [email protected] had the highest ­H2O2 selectivity (81%) and productivity (795 mmol gPd−1 h−1) at atmospheric pressure due to its most substantial shell pore volume of (0.18 ­cm3g−1) and ­H2 adsorption amount. Graphic Abstract

Keywords  Pd hollow catalysts · Shell pore size · Shell pore volume · Direct synthesis of ­H2O2

1 Introduction

* Qian Lin [email protected] Extended author information available on the last page of the article

As ­H2O being its only byproduct, ­H2O2 is considered to be the most eco-friendly oxidant/detergent, and is widely applied in industries such as pulp bleaching and deinking, wastes control, semiconductor cleaning, and soil repair [1].

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Today, the method to produce ­H2O2 in industry is anthraquinone autoxidation process (AO process), whereas, it can produce unwanted wastes and higher operating costs. Compared with AO process, the direct formation of ­H2O2 from ­H2 and ­O2 on the Pd based catalyst undoubtedly has the advantages of simpler process, milder operation conditions (normal pressure and normal/low temperature), lower operating cost and no pollution (water and methanol are usually used as reaction medium) [2]. Nevertheless, this process, so far, cannot achieve industrial production because of its lower selectivity and yield of H ­ 2O2. This can be further explained as follows: (1) O–O bond of H ­ 2O2 and O ­ 2 are likely to be dissociated on active component Pd surface, which produce ­H2O instead of ­H2O2 [3]. (2) utilization rate of ­H2–H2O2 is relative lower because H ­ 2 accumulation amount on Pd surface is smaller due to its lower solubility and adsorption amounts [4, 5]. Freakley et al. [6] pointed out that even if ­H2O2 selectivity reached 96% for the catalysts Pd–Sn/TiO2, its ­H2 conversion rate was merely about 9%. Lee et al. [7] found that despite of an over 90% conversion rate of ­H2, ­H2O2 selectivity was limited to about 8% as the result of the severe side reactions of hydrogenation and H ­ 2O2 decomposition. In summary, improving both the