Sibling rivalry: Cu forces Zn to move somewhere else on mordenite

Significance 

Following recent technological advances, research on the effects of loading zeolites with ion-exchanged or impregnated ions or clusters of two metals has shown that their catalytic activity, stability and selectivity becomes greatly affected. In addition, recent publications have reported on the different scenarios of the two metals’ distribution, chemical state and potential competitive siting. Such studies have pointed out that metal ions with higher charge density occupy small cages and normally prevent another ion migration from supercages. Moreover, it has been seen that preferential ion locations depend on the type of zeolite used. Recently, only T3 sites located in 8-membered ring channels have been observed to selectively perform dimethyl ether carbonylation to methyl acetate, as the others catalyze side reactions and lead to a fast deactivation. Therefore, it is important that the synergetic effects of zinc and copper ions be comprehended since the reaction is of much significance as it offers an iodine-free route to acetic acid or ethanol from dimethyl ether that could be obtained either from methanol or directly from a syngas.

To this note, University of Alberta researchers Allen Reule, Dr. Jing Shen and Professor Natalia Semagina from the Department of Chemical and Materials Engineering assessed the locations of copper and zinc species in the bimetallic ion exchanged mordenite. They hoped the results would potentially explain the previously observed catalytic behavior in dimethyl ether carbonylation that would in turn contribute to the understanding of bimetallic ion exchange on a zeolite. Their work is currently published in the research journal, Chem.Phys.Chem.

In brief, the research method used entailed the characterization of samples comprised of various copper and zinc ratios, by diffuse-reflectance infrared Fourier-transform spectroscopy. Next, pore distribution analysis through argon physisorption, X-ray photoelectron spectroscopy, temperature-programmed reduction and transmission electron microscopy were carried out for the test samples.

The authors observed that in the bimetallic samples, zinc addition resulted in an increase in the coordination strength of copper to the zeolite and prevented copper (II) oxide nanoparticle formation without copper-zinc alloying. Additionally, they noted that copper preferentially exchanged into mordenite as compared to zinc thereby affecting the favorable location of zinc ion-exchange. All in all, the researchers recorded that the effect was achieved at 0.25 copper-zinc molar ratio for the mordenite with a specific silicon-aluminum ratio.

In a nutshell, Professor Natalia Semagina and her colleagues presented the analysis of mordenite samples ion exchanged with copper and zinc ions for the purposes of comprehending metal distribution and its effect on dimethyl ether carbonylation. Generally, it was seen that zinc alone readily exchanged into 8-MR structures (T3 sites), but in the presence of copper, it preferred to exchange into T4 sites in 12-MR structures as opposed to the T3 atoms. Altogether, this led to the conclusion that the selective blockage of T4 sites inhibited the formation of the trimethyl oxonium ion from the adsorbed methyl group and dimethyl ether, and increased the catalyst lifetime during dimethyl ether carbonylation.

Sibling rivalry: Cu forces Zn to move somewhere else on mordenite - Advances in Engineering

About the author

Dr. Allen Reule received his B.Sc. and Ph.D. degrees in Chemical Engineering from the University of Alberta, Canada. He was a member of Dr. Natalia Semagina’s research group from 2013 – 2017, where his research focused on simple and scalable modification of commercially available zeolites for the industrial production of methyl acetate from dimethyl ether carbonylation. His Ph.D. was awarded in 2016 for a thesis entitled “Enhancement of the Stability of Mordenite for use in Dimethyl Ether Carbonylation.” He also performed preliminary research on the oxidative dry reforming of methane, including designing and setting up equipment and executing initial catalyst trials.

His research interests are focused on improving the activity, selectivity, and stability of molecular sieve materials for application as heterogeneous catalysts, adsorbents, and membranes. He is particularly interested in the further study of the competition that occurs when two or more metals are ion-exchanged simultaneously and how that competition can be utilized for catalytic benefit.

He is currently a Research Engineer at the NOVA Chemicals Centre for Applied Research.

About the author

Dr. Jing Shen received her B.Sc. degree in chemical engineering from the University of Alberta. In 2008, she joined Prof. Natalia Semagina’s research group. Since she obtained her Ph.D. degree in 2015, she continued her work as a postdoctoral fellow working in the same group in collaboration with other teams.

Her research focus is heterogeneous catalysis and reaction engineering, comprising the applications of platinum-free ring opening in fuel upgrading, ultra deep sulphur removal in fuel upgrading, methane emission control, dimethyl ether carbonylation, oxidative dry reforming of methane, and photoreduction of CO2.

About the author

Professor Natalia Semagina obtained her undergraduate degree in biotechnology and PhD degree in chemical kinetics and catalysis from the Tver State Technical University in Russia. After several years of service as a senior lecturer and researcher at the same university, she worked as a research associate in the group of catalytic reaction engineering at the Swiss Federal Institute of Technology in Lausanne (EPFL).

In 2008 she joined the University of Alberta, where she now holds a position of Professor at the Department of Chemical and Materials Engineering. Natalia also serves as a Vice-Chair of Catalysis Division of the Chemical Institute of Canada. Her group’s research focuses on experimental heterogeneous catalysis for energy and environment applications.

Reference

Allen A. C. Reule, Jing Shen, Natalia Semagina. Copper Affects the Location of Zinc in Bimetallic Ion-Exchanged Mordenite. Chem.Phys.Chem 2018, volume 19, page 1500– 1506.

Go To Chem.Phys.Chem

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