The incorporation of metal additives into zeolites has allowed a much higher degree of zeolite tunability, including altering the original active sites, introducing new active sites, modifying pore structures, and introducing bifunctional properties. As a result, these modifications have a profound impact on the catalyst performance, altering product selectivity, catalyst activity, and catalyst stability. This thesis investigates the role of several metal additives, including sodium, calcium, cobalt and lanthanum, focusing on their impact during isooctane cracking and aromatic alkylation reaction between toluene and isopropanol. The first part of this thesis explores isooctane cracking over faujasite zeolite as probe enabling the quantification of protolytic cracking, dehydrogenation, and hydrogen transfer pathway. The development of this probe was possible by the addition of metal cations such as Na, Ca, Co as additives to modify the rates of these reaction pathways. This has enabled a quantitative assessment of cation titration at not only promoting new pathways, but selectively titrating sites that are most active for protolytic cracking. We further contrast this simple approach in ternary diagrams that visually depict the contributions of catalyst modifications and reaction conditions on the three parallel reactions, revealing that Na selectively titrates sites responsible for protolytic cracking while Co promotes dehydrogenation reactions. Finally, we reveal that the incorporation of La, often added to Y zeolites in industrial catalytic cracking operations, enhances both hydrogen transfer rates and dehydrogenation rate of alkanes. The second and third part of the thesis primarily focuses on La as an additive. The second part is a continuation of La modified Y zeolite from the first part. This section focuses the impact of La introduction as an additive via ion exchange on the physical and chemical properties of low Si/Al Y zeolite, including the preservation of zeolitic structural integrity and acid sites modifications. The addition of La has a pronounced effect on the isooctane cracking performance of zeolite Y, altering the reaction pathway selectivity and cracking activity. Finally, the final part of the thesis investigates the effects of La incorporation in H-MOR via wetness impregnation and focuses on the impact of La on shape selectivity and catalysts' stability against coking during the alkylation between toluene and isopropanol. The addition of La alters the pore size of the MOR zeolite via pore constriction. Furthermore, La also enhances the hydrogen transfer activity between carbenium ion and coke deposited. This modification leads to improved product selectivity and catalyst stability, highlighting the potential of La-modified zeolites in enhancing catalytic performance. Collectively, these findings deepen our understanding of the role of these additives in zeolite catalysis, offering insights for optimizing catalyst synthesis for hydrocarbon reactions.