Revealing the Effect of Mass Transfer on Direct Dehydrogenation of Ethylbenzene Catalyzed by Phosphorous‐doped Boron Nitride: Comparative Study

Abstract

Phosphorous-doped boron nitride (PBN) was previously confirmed to be an effective metal-free catalyst for the challenging topic of ethylbenzene direct dehydrogenation (DDH) to styrene.Here, the effect of mass transfer factors including the porosity and surface exposure degree of mesoporous-PBN (m-PBN) on its performance over DDH was investigated by control experiments. The central pore size of m-PBN was closely dependent on the thiourea amount and heating rate. The m-PBN with optimal pore size delivered a significantly improved styrene [a] Y.

Improved Catalytic Performance of Direct Dehydrogenation of Ethylbenzene by Creating Boron Defects on Phosphorus‐doped Boron Nitride

“…This is probably related to the synergistic effect of thiourea and barbituric acid, which could form hydrogen bond connection as reported [31] . These changes suggest that the addition of barbituric acid indeed optimizes the pore structure of the catalysts, and will be beneficial to the improvement of mass transfer condition in m‐PBN, according to our previous work [24] …”

“…In our previous paper, we found that phosphorus‐doped h‐boron nitride (PBN) to be an efficient catalyst for DDH of ethylbenzene with N 2 P=O and N 3 P−OH as active sites [23] . In addition, considering the microporous structure of PBN which is disadvantageous to the mass transfer of ethylbenzene molecule, we fabricated the mesoporous PBN (m‐PBN) by thiourea‐assisted synthesis without changing active groups, and obtained significantly improved ethylbenzene conversion rate and stability [24,25] . As we know, in the process of hybrid‐doping or pore‐forming, the structural defects of the materials are always inevitable to be created.…”

“…PBN and m-PBN were prepared by a method described in previous reports. [23,24] The B-defected PBN and m-PBN were prepared as follows. Boric acid (0.4 g), urea (9.3 g), etidronic acid monohydrate (HEDP, 0.93 g) and a specific amount of barbituric acid were dissolved in 40 mL water to form a clear solution.…”

“…changes suggest that the addition of barbituric acid indeed optimizes the pore structure of the catalysts, and will be beneficial to the improvement of mass transfer condition in m-PBN, according to our previous work. [24] To identify the defects in the newly synthesized catalysts, EPR was used to provide valuable fingerprinting information regarding trapped electrons and surface defects. The EPR spectra of PBN, D-PBN-1.5, m-PBN and D-m-PBN-1.5 samples are shown in Figure 5.…”

“…[23] In addition, considering the microporous structure of PBN which is disadvantageous to the mass transfer of ethylbenzene molecule, we fabricated the mesoporous PBN (m-PBN) by thiourea-assisted synthesis without changing active groups, and obtained significantly improved ethylbenzene conversion rate and stability. [24,25] As we know, in the process of hybrid-doping or pore-forming, the structural defects of the materials are always inevitable to be created. However, as for the two materials of PBN and m-PBN, except the difference of pore structure, no obvious difference of the element content and the species constitution could be identified, which brought difficulty for the analysis and discussion of defects therein.…”