**4. Conclusions**

In conclusion, the effects of synthesis parameters on the crystallization profiles of K-MER zeolite have been investigated. The results reveal that the chemical composition of hydrogel (silica content, water concentration, and mineralizer loading), hydrothermal synthesis time and temperature are found to have many profound effects on the physico-chemical properties of the solid samples such as nucleation and crystallization rates, crystallite size, crystalline phase, purity and morphological properties. By carefully tuning the synthesis conditions, K-MER zeolites with four distinct morphologies, namely nanorod, bullet-like, prismatic and wheatsheaf-like shapes, have been successfully prepared. Furthermore, the influence of morphological properties of K-MER zeolites on their catalytic behavior has also been investigated. The results reveal that K-MER zeolite with nanorod shape gives the best catalytic performance in the cyanoethylation of methanol (94.1%) where its catalytic activity is associated with its stronger and higher number of accessible basic sites located at the external surface. Hence, from a material engineering point of view, this work not only provides an insight on the crystallization process of zeolite but also provides insights on designing zeolites with specific morphologies for advanced applications such as high throughput membranes for catalysis and selective gas separation.

**Author Contributions:** Y.-W.C.: Performed most of the experiments, wrote the manuscript; F.K., T.C.L. and E.-P.N.: wrote and proof-read the manuscript supervised; Y.-W.C.; conceived the entire project, applied for research funding; K.-L.W. and B.S.O.: ran XRD, SEM investigation, proofread the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** The financial support from a FRGS (203/PKIMIA/6711642) grant is gratefully acknowledged. Y.-W. Cheong would also like to thank the USM Fellowship for the scholarship provided.

**Conflicts of Interest:** The authors declare no conflict of interest.
