The isopropylation of naphthalene with propene over H-mordenite: The catalysis at the internal and external acid sites

The isopropylation of naphthalene (NP) with propene over H-Mordenite (MOR) was studied under a wide range of reaction parameters: temperature, propene pressure, period, and NP/MOR ratio. Selective formation of 2,6-diisopropylnaphthalene (2,6-DIPN) was observed at reaction conditions, such as at low reaction temperature, under high propene pressure, and/or with high NP/MOR ratio. However, the decrease in the selectivities for 2,6-DIPN was observed at reaction conditions such as at high temperature, under low propene pressure, and/or with low NP/MOR ratio. The selectivities for 2,6-DIPN in the encapsulated products were remained high and constant under all reaction conditions. These results indicate that the selective formation of 2,6-DIPN occurs through the least bulky transition state due to the exclusion of the bulky isomers by the MOR channels. The decrease in the selectivities for 2,6-DIPN are due to the isomerization of 2,6-DIPN to 2,7-DIPN at the external acid sites, directing towards thermodynamic equilibrium of DIPN isomers

Morphological control of mesoporous CN based hybrid materials and their excellent CO2 adsorption capacity

Highly ordered mesoporous carbon nitrides (MCN-1-Ts) with uniform rod shaped morphology have been synthesized by a hard templating technique using SBA-15 silicas prepared a under hydrothermal "static" condition at different temperatures as templates following a simple polymerization reaction between carbon tetrachloride (CTC) and ethylenediamine (EDA) inside the large pores of SBA-15. The static hydrothermal condition offers uniform rod shaped morphology for the template materials which has been completely replicated into the MCN nanostructures. The obtained materials were characterized with low angle XRD, N2 adsorption, high resolution transmission electron microscopy, high resolution scanning electron microscopy (FE SEM), Fourier transform infra-red (FT-IR), and X-ray photoelectron spectroscopy (XPS). The characterization results confirm the successful replication of the ordered structure, morphology and mesoporosity of the template material into carbon nitride. The FT-IR and XPS techniques confirm the presence of free -NH and -NH2 groups on the surface of MCN, which are critical for capturing CO2. Finally, these materials with high surface area and uniform morphology are used as adsorbents for high pressure CO2 adsorption at different temperatures of 0, 10 and 25 °C. It is found that the morphology of the materials which has a direct relation with the textural parameters plays a significant role in enhancing the amount of CO2 adsorption. The MCN with the uniform morphology and the highest surface area registers the highest CO2 adsorption capacity (16.5 mmol g-1) at 0 °C and 30 bar pressure, which is found to be higher than that of the previously reported 3D- cage type MCN, activated carbon, multiwalled carbon nanotubes and mesoporous silicas

Photocatalytic hydrogen generation from water using a hybrid of graphene nanoplatelets and self doped TiO2-Pd

Nanohybrids of self doped (Ti doped or reduced TiO -TiOR) TiO-graphene nanoplatelets (TiO R-G) of different compositions are synthesized by a facile soft chemical method. A decrease of bandgap and improved visible light absorption is exhibited by TiOR-G. Based on current-voltage (I-V) measurements, it is concluded that the hybrid material possesses improved electron transport properties compared to TiOR and pure TiO. A detailed characterization of the composites indicated that TiOR exists as a dispersed phase on graphene nanoplatelets (graphene). Among different compositions of the composites, the catalyst containing 3 weight% of graphene (TiOR-3G) shows enhanced photocatalytic activity for hydrogen generation from water compared to both TiO and TiOR. When Pd is used as co-catalyst in this composite, a large increase in the activity is observed. The increased efficiency of the nanocomposite is attributed to factors like: (i) improved visible light absorption promoted by G and Ti dopant (ii) increased lifetime of the charge carriers assisted by the enhanced electron transporting properties of G (iii) increased number of active sites for hydrogen evolution provided by the Pd co-catalyst. This work highlights the role of TiO based hybrid materials as efficient photocatalysts for solar energy utilization. This journal i

Mesoporous non-siliceous materials and their functions

Research on the synthesis and the application of mesoporous non-siliceous materials is an emerging area attracting a lot of attention by researchers in the field. It is rapidly growing because of the existence of a lot of opportunities in the design, the synthesis, and potential applications of novel non-siliceous materials. This chapter presents an overview of the advances in the synthesis of mesoporous non-siliceous materials such as metal oxides, metals, semiconductors, polymers, carbons, and nitrides. Mostly, soft- and hard-templating methods have been used for the preparation of the non-siliceous mesoporous materials. Using the soft-templating approach and varying the synthesis conditions, surfactant concentration, solution pH, and the temperature, the structure and the textural parameters of the mesoporous non-siliceous materials can be controlled. Mesoporous metals are a fascinating group of materials derived through the soft-templating approach, and they are promising for the production of sensors, fuel cell supports, electronics, optics, and catalysts, since they possess a high specific surface area, conductivity, and a well-ordered porous structure. Some of the possible applications of these materials are addressed in this chapter

Shape-Selective Catalysis in the Alkylation of Naphthalene: Steric Interaction with the Nanospace of Zeolites

Steric interaction of reagents with nanospace of zeolites was studied in alkylation: isopropylation, sec-butylation, and tert-butylation of naphthalene (NP) over several large-pore zeolites to elucidate the mechanism of shape-selective catalysis. Selectivities for β,β- and 2,6-dialkylnaphthalene (DAN) were influenced by the type of zeolite and bulkiness of alkylating agent. Shape-selective formation of β,β- and 2,6-diisopropylnaphthalene (DIPN) occurred only over H-mordenite (MOR) in the isopropylation of NP. Bulky α,α- and α,β-DIPN are excluded because of steric restriction at their transition states by the MOR channels, resulting in the selective formation of β,β- and 2,6-DIPN. AFI (SSZ-24) gave also high selectivities for 2,6-DIPN, and CFI (CIT-5) and MSE (MCM-68) gave high selectivities for β,β-DIPN. The lower selectivities for 2,6-DIPN were observed over the zeolites, ATS (SSZ-55), IFR (SSZ-42), DON (UTD-1), SFH (SSZ-53), FAU (Y-zeolite), BEA (zeolite β), and CON (CIT-1). Their channels allow the accommodation of bulky isomers, resulting in the catalysis under kinetic and/or thermodynamic controls. The selectivities for β,β- and 2,6-DAN were enhanced with the increase in bulkiness of alkylating agents: 1-butene for sec-butylation and 2-methylpropene for tert-butylation, even over zeolites with large pores and channels: the transition states of the least bulky isomers only fit the channels, and the other bulky isomers are excluded by steric restriction of the channels. However, tert-butylation over FAU, BEA, and CON had selectivities of around 50-60% for 2,6-DTBN, and almost 100% selectivities for β,β-DTBN. These zeolites cannot recognize the differences between 2,6- and 2,7-DTBN, but they can differentiate β,β-DTBN from the other isomers. The results indicate that the fitting of the least bulky isomers to zeolite channels, resulting in the exclusion of other bulky isomers, is a key for highly shape-selective catalysis

Alkylation of biphenyl over zeolites: shape-selective catalysis in zeolite channels

Steric interaction of reactants, products, and transition state intermediates with zeolites with 12- and 14-membered ring pore entrances is discussed in the alkylation of biphenyl (BP) by propene, 1-butene, and 2-methylpropene as alkylating agents. The selectivities for the least bulky 4,4′-dialkylbiphenyl (4,4′-DAB) depended on\ua0the types of zeolite and alkylating agent. The zeolites are classified as two types: Category I: mordenite (MOR), SSZ-24 (AFI), SSZ-31 (STO), CIT-5 (CFI), MCM-68 (MSE), and ZSM-12 (MTW) with straight (or slightly corrugated) channels with 12-MR or 14-MR pore entrances. Category II: SSZ-42 (IFR), SSZ-55 (ATS), SSZ-60 (SSY), Y (FAU), β (BEA), CIT-1 (CON), UTD-1 (DON), and SSZ-53 (SFH) with large channels. Category I zeolites have shape-selective natures in their channels in the isopropylation. Among them, MOR supported the highest selectivities around 85\ua0% for 4,4′-diisopropylbipneyl (4,4′-DIPB) at moderate temperatures\ua0as 250 C. The selectivities of 4,4′-DIPB are: MOR\ua0>\ua0AFI, MSE\ua0>\ua0MTW, CFI, STO: the differences are due to the recognition of 4,4′- and 3,4′-DIPB by the channels. Category II zeolites allow the accommodation and the formation of bulky DIPB isomers in their channels, resulting in non-shape selective catalysis under kinetic and/or thermodynamic controls. Bulky alkylating agents, 1-butene and 2-methylpropene, enhance selective formation of the least bulky 4,4′-DAB: 4,4′-di-sec-butylbiphenyl (4,4′-DSSB) and 4,4′-di-tert-butylbiphenyl (4,4′-DTBB), respectively, even over Category II zeolites. The bulky moieties enhance the exclusion of bulky isomers by their interaction with zeolite channels. The selectivities for 4,4′-DSSB were increased remarkably to higher than 80\ua0% for Category I zeolites and to 70\ua0% for ATS in Category II zeolites\ua0in the sec-butylation. However, kinetic and thermodynamic controls still worked with the formation of bulky isomers over Category II zeolites: IFR, FAU, BEA, CON, DON, and SFH in\ua0the sec-butylation. The high selectivities for 4,4′-DTTB higher than 80\ua0% were observed for the zeolites, except FAU in the tert-butylation. These results indicate that the selectivities for 4,4′-DAB are controlled primarily by space and shape of zeolite channels for active sites, and not always by the size of pore entrances

Comparison of the mechanical stability of cubic and hexagonal mesoporous molecular sieves with different pore sizes

The mechanical stability of mesoporous molecular sieves, viz. MCM-41, MCM-48, SBA-1 and SBA-15, is compared employing X-ray powder diffraction, nitrogen and organics adsorption. The adsorption capacity is considerably decreased by mechanical compression between 20 and 400 MPa. It has been found that SBA-1 exhibits the highest mechanical stability, while SBA-15 is mechanically unstable despite its thick walls (ca. 2 nm)