Jiafeng Yu

Synthesis of a zeolite membrane as a protective layer on a metallic Pd composite membrane for hydrogen purification

Palladium composite membranes are used widely in the hydrogen purification process owing to their excellent hydrogen permeability and selectivity. However, they can lose hydrogen permeability irreversibly when exposed to a small amount of impurity gases, which severely limits their applications. Here, a seed-free hydrothermal method was developed to synthesize a zeolite membrane on the surface of an ultra-thin metallic Pd composite membrane to offer protection from impurity gases. The impurity gases with a kinetic diameter larger than the zeolite pore size were prevented from coming in direct contact with the Pd composite membrane. The presence of a protective zeolite membrane distinctly suppressed the hydrogen permeance decline in a 5% propylene/hydrogen mixture, which greatly enhanced the stability of the Pd membrane. SEM and XRD showed that the acid pretreatment before the secondary hydrothermal growth process and the rotary state were beneficial for synthesizing thin and uniform zeolite membranes. With increasing synthesis time, the protective effects of the zeolite membrane were enhanced significant due to the reduction of defects.

The Unique Role of CaO in Stabilizing the Pt/Al2O3 Catalyst for the Dehydrogenation of Cyclohexane

Coke‐induced deactivation is one of the major challenges in the field of heterogeneous catalysis. Herein, the performance of the Pt/Al2O3 catalyst for the hydrogen‐free dehydrogenation of cyclohexane was improved by doping with a small amount of Ca. The Ca‐modified Pt/Al2O3 catalyst exhibited a cyclohexane conversion of 97.0 % and maintained a conversion above 75 % after 48 h, whilst the unmodified catalyst was deactivated from 87.0 to 2.7 % under the same conditions. Characterization techniques, including in situ DRIFT, XPS, thermal analysis, and temperature‐programmed techniques, revealed that the presence of Ca effectively suppressed the deep dehydrogenation of H‐rich carbonaceous components and promoted coke desorption by increasing the H/C ratio of H‐deficient coke. This promotion effect of Ca was also associated with neutralizing the residual Cl ions and promoting immediate dehydrogenation.

Highly sulfur-tolerant Pd composite membranes with a protective layer of MoS2/γ-alumina

Sulfur-tolerant Pd-based composite membranes were produced by coating a thin layer of MoS2/γ-alumina on the membrane surface. This layer acted as an “armor” to prevent H2S from directly contacting the Pd membrane surface by preferentially adsorbing and decomposing the H2S.

“Modified” Liquid–Liquid Displacement Porometry and Its Applications in Pd-Based Composite Membranes

For H2 separation by Pd-based composite membranes, the pore mouth size distribution of the porous support immediately affects the quality of the deposited layer, including continuity and defect/pinhole formation. However, there is a lack of convenient and effective methods for characterization of pore mouth size of porous supports as well as of defect distribution of dense Pd-based composite membranes. Here we introduce a novel method by modifying conventional liquid–liquid displacement porometry. When the pore tunnels are filled with Liquid B and the outer surface is occupied by Liquid A, the reopening of the pore mouth depends on the pressure of Liquid B and the interfacial tension at the position of the pore mouth, from which the pore mouth size can be determined according to the Young–Laplace equation. Our experimental tests using this method with model samples show promising results, which are well supported by those obtained using FESEM (fild emission scanning electron microscope), AFM (atomic force microscope), and conventional liquid–liquid displacement porometry. This novel method can provide useful information for not only surface coatings on porous substrates but also for modification of dense membrane defects; thus, broad utilizations of this technique can be expected in future study.