With the increasingly intense competition in the lubricant market, improving product quality is paramount for sustaining a competitive edge
[1−2]. The hydroisomerization of
n-alkanes to branched alkanes, characterized by high lubricant base oil yield
[3], low viscosity and evaporation loss, superior oxidation stability, and good low-temperature fluidity
[4−5], is an effective strategy for enhancing lubricant quality
[6−7]. Consequently, optimizing the hydroisomerization performance of
n-alkanes is critical for the production of high-quality lubricants
[8−9]. Ideally, this process is driven by bifunctional catalysts, which combine metallic and acidic functions
[10]. The metal sites, typically provided by noble metals (e.g., Pt, Pd) or non-noble metals (e.g., Co, Ni), facilitate hydrogenation/dehydrogenation, while the acid sites—derived principally from zeolites, amorphous silica-alumina, organic-inorganic hybrids, or metal oxides—catalyze skeletal isomerization
[11]. Among them, zeolite molecular sieves have been widely used as catalyst supports for
n-alkane hydroisomerization, such as SAPO molecular sieves
[12−14], aluminosilicate zeolites
[15−17], and mesoporous molecular sieves
[18−20].
n-Alkanes and
iso-alkenes undergo dehydrogenation and hydrogenation reactions on the metal sites, respectively, while
n-alkenes undergo protonation and skeletal isomerization on the acid sites. The isomerization process typically proceeds
via two reaction mechanisms: the “pore-mouth” type and the “key-lock” type
[21−22]. The “pore-mouth” mechanism restricts the reaction to the channel entrance, favoring terminal methyl-branched isomers
[23]. In contrast, the “key-lock” mechanism allows the alkane chain to align within the pore channel, selectively yielding centrally branched isomers
[24].
In recent years, composite zeolites have been extensively investigated due to their unique properties. Formed by combining two or more distinct zeolite phases
via physical or chemical methods, these materials not only retain the intrinsic characteristics of their individual components but often exhibit synergistic effects that surpass the performance of single-phase zeolites. Currently, the synthesis methods for composite zeolites mainly include: seed-assisted method, mechanical mixing, one-step crystallization, two-step crystallization
[25] and director-assisted reassembly method
[26], among others. Among these methods, mechanical mixing is widely favored for its cost-effectiveness, operational simplicity, and the ability to precisely control component ratios while preserving the structural integrity of the individual zeolites. Several studies have validated the efficacy of this method. For instance, Zhang et al.
[27] mechanical mixing is widely favored for its cost-effectiveness, operational simplicity, and the ability to precisely control component ratios while preserving the structural integrity of the individual zeolites. Several studies have validated the efficacy of this method; Similarly, Liu et al.
[28] found that mixing Al-SBA-15 zeolite with USY zeolite reduced acid amount but significantly enhanced catalytic performance, achieving 99% selectivity for perhydroanthracene; Furthermore, Fan et al.
[29] demonstrated that a ZSM-5/SAPO-11 mixture possessed increased mesoporosity, which could accelerate mass diffusion, and exhibited a moderate acidity distribution with more pronounced synergy between Brønsted acid and Lewis acid sites.
ZSM-22 (TON topology, 0.45 nm × 0.55 nm) and ZSM-23 (MTT topology, 0.45 nm × 0.56 nm) possess similar one-dimensional 10-membered ring channels. Therefore, combining these two zeolites can integrate the advantages of both TON and MTT structures, potentially leading to superior hydroisomerization performance. Currently, methods for synthesizing ZSM-22-ZSM-23 composite zeolites mainly include hydrothermal synthesis
[30], microwave-assisted synthesis
[31], and low-template ultrasonic-assisted synthesis. However, these methods generally suffer from harsh conditions and difficulties in scale-up production. In this work, a ZSM-22-ZSM-23 composite was prepared
via a facile mechanical mixing route. Its synergistic effects in the hydroisomerization of
n-dodecane and its influence on the isomer distribution were investigated, and its catalytic performance was compared with that of the individual zeolites.