Comments on “Influence of Zeolite Protective Overlayer on the

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Comments on “Influence of Zeolite Protective Overlayer on the Performances of Pd Thin Film Membrane on Tubular Asymmetric Alumina Supports” Jiafeng Yu* Dalian Institute of Chemical Physics, Chinese Academy of SciencesDalian National Laboratory for Clean Energy, Zhongshan Road 457#, Dalian, Liaoning 116023, China ecently, a paper has been published in Industrial & Engineering Chemistry Research, titled “Influence of Zeolite Protective Overlayer on the Performances of Pd Thin Film Membrane on Tubular Asymmetric Alumina Supports” (DOI: 10.1021/acs.iecr.6b00690).1 I have noticed that the authors mentioned the work of Yu et al.,2 “Synthesis of Zeolite Membrane as a Protective Layer on Metallic Pd Composite Membrane for Hydrogen Purification” (J. Mater. Chem. A, 2015, 3, 5000; referenced in the paper as ref 18), many times and some of the statements are in dispute. I have the following two comments on this paper: (1) In the “Introduction” of this paper, they mentioned that “Xu et al.18 proposed recently the use of a zeolite protective layer on the thin Pd membrane layer to improve stability in propane dehydrogenation, although the H2 permeance decreases about 60% in 7 h of reaction in the zeolite−Pd composite membrane at 400 °C”. Those authors also mentioned, in Section 3.4 of that paper, that “It may be noted that Yu et al.18 reported for zeolite−Pd composite membranes (with the zeolite layer constituted by a mixture of NaA, hydroxy sodalite, and Z-21), in tests at 400 °C by feeding a 5% propane/hydrogen mixture, a loss of permeance of 56% in 7 h for the best sample.” They did not state the source of the H2 permeance reduction data (i.e., 60% and 56%). In contrast, I noticed that, in ref 18, the H2 permeance reduction in 7 h of pure Pd membrane and zeolite-Pd membrane are 45.8% and 18.5%, respectively, which are clearly shown in Table 1 of ref 18. Moreover, specific instructions about the results of H2 permeance tests are shown in Page 5004 of ref 18, stating that “In the period of 420 min exposure to mixture gases, the hydrogen permeance of Pd membrane without zeolite membrane protection quickly declined from 111.4 to 60.4 mol/m2·h·bar (45.8 % reduction). While zeolite-3h and zeolite6h slowly declined from 115.5 to 72.2 mol/m2·h·bar (37.5 % reduction) and 113.7 to 92.7 mol/m2·h·bar (18.5 % reduction), respectively.” However, the authors emphasized that the loss of permeance of the best sample in ref 18 was 56%. This number is even larger than that of the pure Pd membrane without any protection. (2) Also in Section 3.4 in this paper, the authors mentioned that “When we feed a similar mixture (e.g., 5% propane in H2 instead of 20% propylene in H2) to M8 membrane, no deactivation was observed in our case” and “we used 20% propylene instead of 5% propane as in Yu et al.’s 18 experiments”. In the “Conclusions” section of this paper, the authors also state that “An increased stability was observed, but deactivation is still present in accelerated tests using a high propylene (20%) mixture in H2 rather than 5% propane in

hydrogen, as previously reported.18” The authors have compared their results based on 20% propylene in H2 mixture to the results based on 5% propane in H2 mixture in ref 18 many times and concluded that their TS-1/Pd/Al 2 O 3 composite membrane showed better stability. In fact, the mixture that is tested in ref 18 is 5% propylene in H2 but not 5% propane in H2. In ref 18, they referred to the word “propylene” 18 times in the entire paper but only make one spelling mistake in the caption of Figure 5. For example, the authors of ref 18 stated that “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.” in the Abstract and “The initial H2 permeance and the H2 permeance after introduction of 5 % propylene/hydrogen mixtures (200 mL/min) were measured at 400 °C.” in the Experimental Section. In addition, they also declared that, in the discussion of the H2 permeance results, and in the description of Figure 5 as “Then the 5 % propylene/hydrogen mixtures (200 mL/min) are introduced into membrane reactor.” and “The hydrogen permeance was plotted as a function of the exposure time to 5 % propylene/hydrogen mixtures in Fig. 5.”, respectively.

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© XXXX American Chemical Society

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Abate, S.; Diaz, U.; Prieto, A.; Gentiluomo, S.; Palomino, M.; Perathoner, S.; Corma, A.; Centi, G. Influence of Zeolite Protective Overlayer on the Performances of Pd Thin Film Membrane on Tubular Asymmetric Alumina Supports. Ind. Eng. Chem. Res. 2016, 55, 4948−4959. (2) Yu, J.; Qi, C.; Zhang, J.; Bao, C.; Xu, H. Synthesis of a zeolite membrane as a protective layer on a metallic Pd composite membrane for hydrogen purification. J. Mater. Chem. A 2015, 3, 5000−5006.

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DOI: 10.1021/acs.iecr.6b01716 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX