1,3-Butadiene Adsorption over Transition Metal Polycation Exchanged Faujasites

Preparation of Functionalized Zr-Based MOFs and MOFs/GO for Efficient Removal of 1,3-Butadiene from Cigarette Smoke

Removal of 1,3-butadiene from cigarette smoke plays an important role in human health and environmental protection. Herein, a series of UiO-66 X% containing different ratios of the -NH₂ group was synthesized via the solvothermal method by using terephthalic acid (H₂BDC) and 2-aminoterephthalic acid (NH₂-BDC) as ligands. Using GO as support, a series of UiO-66-NH₂/GO Y% were prepared by controlling the ratio of UiO-66-NH₂ and GO. The effects of -NH₂ and GO contents on the structure and composition of MOFs were investigated. Finally, the different -NH₂ contents of UiO-66 X% and the different GO contents of UiO-66-NH₂/GO Y% were applied in 1,3-butadiene removal from cigarette smoke. The results showed that UiO-66 X% with the higher contents of -NH₂ showed a higher rate of 1,3-butadiene removal, and UiO-66-NH₂/GO Y% with the GO contents of 5% showed the highest removal rate of about 33.85%, which was 25.54% higher than that of activated carbon. In addition, the saturation capacity of the adsorbent materials for 1,3-butadiene was as high as 210.01-239.54 mg/g, showing great potential in reducing harmful components in cigarette smoke and environmental protection.

Catalytic conversion of ethene to butadiene or hydrogenation to ethane on HY zeolite-supported rhodium complexes: Cooperative support/Rh-center route

Rh(C₂H₄)₂ species grafted on the HY zeolite framework significantly enhance the activation of H₂ that reacts with C₂H₄ ligands to form C₂H₆. While in this case, the simultaneous activation of C₂H₄ and H₂ and the reaction between these species on zeolite-loaded Rh cations is a legitimate hydrogenation pathway yielding C₂H₆, the results obtained for Rh(CO)(C₂H₄)/HY materials exposed to H₂ convincingly show that the support-assisted C₂H₄ hydrogenation pathway also exists. This additional and previously unrecognized hydrogenation pathway couples with the conversion of C₂H₄ ligands on Rh sites and contributes significantly to the overall hydrogenation activity. This pathway does not require simultaneous activation of reactants on the same metal center and, therefore, is mechanistically different from hydrogenation chemistry exhibited by molecular organometallic complexes. We also demonstrate that the conversion of zeolite-supported Rh(CO)₂ complexes into Rh(CO)(C₂H₄) species under ambient conditions is not a simple CO/C₂H₄ ligand exchange reaction on Rh sites, as this process also involves the conversion of C₂H₄ into C₄ hydrocarbons, among which 1,3-butadiene is the main product formed with the initial selectivity exceeding 98% and the turnover frequency of 8.9 × 10^-3 s^-1. Thus, the primary role of zeolite-supported Rh species is not limited to the activation of H₂, as these species significantly accelerate the formation of the C₄ hydrocarbons from C₂H₄ even without the presence of H₂ in the feed. Using periodic density functional theory calculations, we examined several catalytic pathways that can lead to the conversion of C₂H₄ into 1,3-butadiene over these materials and identified the reaction route via intermediate formation of rhodacyclopentane.

Catalytic activation of ethylene C–H bonds on uniform d8 Ir(i) and Ni(ii) cations in zeolites: toward molecular level understanding of ethylene polymerization on heterogeneous catalysts

The long-debated intermediates of ethylene polymerization are revealed using uniform d⁸ metal ions in zeolites.

Controlling guest conformation for efficient purification of butadiene

Conventional adsorbents preferentially adsorb the small, high-polarity, and unsaturated 1,3-butadiene molecule over the other C₄ hydrocarbons from which it must be separated. We show from single-crystal x-ray diffraction and computational simulation that a hydrophilic metal-organic framework, [Zn₂(btm)₂], where H₂btm is bis(5-methyl-1H-1,2,4-triazol-3-yl)methane, has quasi-discrete pores that can induce conformational changes in the flexible guest molecules, weakening 1,3-butadiene adsorption through a large bending energy penalty. In a breakthrough operation at ambient temperature and pressure, this guest conformation-controlling adsorbent eluted 1,3-butadiene first, then butane, butene, and isobutene. Thus, 1,3-butadiene can be efficiently purified (≥99.5%) while avoiding high-temperature conditions that can lead to its undesirable polymerization.

Sustainable Separations of C4 -Hydrocarbons by Using Microporous Materials

Petrochemical refineries must separate hydrocarbon mixtures on a large scale for the production of fuels and chemicals. Typically, these hydrocarbons are separated by distillation, which is extremely energy intensive. This high energy cost can be mitigated by developing materials that can enable efficient adsorptive separation. In this critical review, the principles of adsorptive separation are outlined, and then the case for C₄ separations by using zeolites and metal-organic frameworks (MOFs) is examined. By analyzing both experimental and theoretical studies, the challenges and opportunities in C₄ separation are outlined, with a focus on the separation mechanisms and structure-selectivity correlations. Zeolites are commonly used as adsorbents and, in some cases, can separate C₄ mixtures well. The pore sizes of eight-membered-ring zeolites, for example, are in the order of the kinetic diameters of C₄ isomers. Although zeolites have the advantage of a rigid and highly stable structure, this is often difficult to functionalize. MOFs are attractive candidates for hydrocarbon separation because their pores can be tailored to optimize the adsorbate-adsorbent interactions. MOF-5 and ZIF-7 show promising results in separating all C₄ isomers, but breakthrough experiments under industrial conditions are needed to confirm these results. Moreover, the flexibility of the MOF structures could hamper their application under industrial conditions. Adsorptive separation is a promising viable alternative and it is likely to play an increasingly important role in tomorrow's refineries.