Weiping Zhang

Structurally Designed Synthesis of Mechanically Stable Poly(benzoxazine-co-resol)-Based Porous Carbon Monoliths and Their Application as High-Performance CO2 Capture Sorbents

Porous carbon monoliths with defined multilength scale pore structures, a nitrogen-containing framework, and high mechanical strength were synthesized through a self-assembly of poly(benzoxazine-co-resol) and a carbonization process. Importantly, this synthesis can be easily scaled up to prepare carbon monoliths with identical pore structures. By controlling the reaction conditions, porous carbon monoliths exhibit fully interconnected macroporosity and mesoporosity with cubic Im3m symmetry and can withstand a press pressure of up to 15.6 MPa. The use of amines in the synthesis results in a nitrogen-containing framework of the carbon monolith, as evidenced by the cross-polarization magic-angle-spinning NMR characterization. With such designed structures, the carbon monoliths show outstanding CO(2) capture and separation capacities, high selectivity, and facile regeneration at room temperature. At ~1 bar, the equilibrium capacities of the monoliths are in the range of 3.3-4.9 mmol g(-1) at 0 °C and of 2.6-3.3 mmol g(-1) at 25 °C, while the dynamic capacities are in the range of 2.7-4.1 wt % at 25 °C using 14% (v/v) CO(2) in N(2). The carbon monoliths exhibit high selectivity for the capture of CO(2) over N(2) from a CO(2)/N(2) mixture, with a separation factor ranging from 13 to 28. Meanwhile, they undergo a facile CO(2) release in an argon stream at 25 °C, indicating a good regeneration capacity.

Insights into the Correlation of Aluminum Distribution and Brönsted Acidity in H-Beta Zeolites from Solid-State NMR Spectroscopy and DFT Calculations

Here we utilized 27Al MAS/MQMAS and 31P MAS NMR of quantitative adsorption of trimethylphosphine oxide (TMPO) and DFT calculations to elucidate the relationship between Al distribution and Brönsted acidity of series H-Beta zeolites derived from dealumination of Al-rich H-Beta zeolite. Three types of Brönsted acid strengths corresponding to different specific Al T-sites were demonstrated. The removal of one framework Al in 5MR2--2Al and 6MR-2Al sites led to increasing the Brönsted acid strength of dealuminated H-Beta. Our findings on such exact correlation between specific Al distributions and corresponding Brönsted acid sites may guide the controlling Al distribution to get desired acid properties through zeolite synthesis or finely tuned dealumination, which has a great impact on the catalytic activity and selectivity of zeolite catalysts.

Al Location and Acid Strength in Al-rich Beta Zeolite Catalyst: A Combined Density Functional Theory and Solid-state NMR Study

Density functional theory was performed to investigate the specific Al distribution and the origination of Brönsted acid strength in the Al‐rich Beta zeolite catalyst. The most preferable sites for Al atoms of Al‐rich and Si‐rich Beta zeolites represented by 1Al and 2Al atoms are compared by electrostatic potential analysis and substitution energies. IT1 and T9 sites are the most favorable locations for 1Al distribution, while 5MR1‐T92, 5MR2‐T15 and 6MR1‐T66 sites are inclined to be occupied by Al atoms for 2Al distribution. Al atoms in 5MR1‐T17 sites would be dealuminated more easily to become the extra‐framework Al species when Al‐rich Na‐Beta is ion‐exchanged to H‐Beta. As for NNNN sequences in Al‐rich Beta, 6MR1‐T66 sites are the most easily substituted by Al atoms, facing different channels and showing the properties of isolated Al site. Proton affinities, NH3 adsorption energies and 1H chemical shifts of [D5]pyridine adsorbed in Beta zeolites were used to analyze the Brönsted acidity. Si‐rich Beta has stronger Brönsted acid strength than the Al‐rich counterpart. This agrees with the experimental results from 1H MAS NMR with [D5]pyridine as probe molecule. The Brönsted acid strength of Al‐rich and Si‐rich H‐Beta zeolites was correlated to the Al location at the specific T‐site on the zeolitic framework.

Pd Nanoparticles Encapsulated in FER Zeolite through a Layer Reassembling Strategy as Shape-selective Hydrogenation Catalyst

Noble metal nanoparticles (NPs) encapsulated in zeolites bearing distinct shape‐selective properties at molecular level expand their new applications in catalysis. Here we report a synthesis strategy for the encapsulation of Pd NPs inside FER zeolite via a layer reassembling process. Pd precursors were introduced by swelling FER layers in RUB‐36 through the surfactant cetyltrimethylammonium cations (CTA+) and then an ion‐exchange process at ambient temperature. Pd@FER was formed with a uniform diameter distribution of Pd NPs at about 1.4u2005nm during the topotactic transformation from layered zeolite precursors to 3‐dimensional zeolites followed by calcination. The as‐prepared Pd@FER catalyst exhibits distinct shape‐selective properties in hydrogenation reactions. It has relatively lower activity for 1‐hexene and almost no activity for 1‐phenyl‐1‐cyclohexene compared with Pd/RUB‐37 catalyst prepared via wet impregnation due to the restrictions of channels in the FER zeolite. On the contrary, Pd@FER shows very high hydrogenation activity for benzaldehyde and very low activity for diphenylmethanone hydrogenation, while Pd/RUB‐37 exhibits high hydrogenation activity for both benzaldehyde and diphenylmethanone. This synthesis strategy may be extended to other noble metals or two‐dimensional layered zeolite systems for size‐selective hydrogenation reactions.

Methane activation over a boron nitride catalyst driven by in situ formed molecular water

Boron nitride can catalyze the oxidative conversion of methane to valuable chemicals with minor formation of CO2. B–O–H groups, both originally existing and in situ generated in the reaction, promote the activation of O2 and CH4, and a novel H2O-assisted O2 and CH4 synergetic mutual activation mechanism was proposed.

Excellent Performances of Dealuminated H-Beta Zeolites from Organotemplate-Free Synthesis in Conversion of Biomass-derived 2,5-Dimethylfuran to Renewable p-Xylene

Direct synthesis of renewable p-xylene (PX) by cycloaddition of biomass-derived 2,5-dimethylfuran (2,5-DMF) and ethylene was achieved over Al-rich H-beta zeolites synthesized by an organotemplate-free approach and their dealuminated counterparts with different Si/Al ratios. Among them, H-beta zeolite with an Si/Al ratio of 22, obtained from an Al-rich parent by dealumination, was found to be an excellent catalyst for the synthesis of PX. A PX yield of 97u2009% and 2,5-DMF conversion of 99u2009% were obtained under optimized conditions. These results are even better than those of a commercial H-beta zeolite prepared using a organotemplate synthesis with a similar Si/Al ratio of 19. The excellent performance of the H-beta zeolite with Si/Al ratio of 22 is closely related to its acidity and porous structure. A moderate Brønsted/Lewis acid ratio can improve the conversion of 2,5-DMF to as high as 99u2009%. Furthermore, dealuminated H-beta zeolite has a secondary pore system that facilitates product diffusion, which increases the selectivity to PX. In addition, this catalyst shows better regeneration. After five successive regeneration cycles, the yield of PX was still as high as 85u2009% without obvious dealumination. This work provides a deeper understanding of the more general Diels-Alder cycloaddition of furan-based feedstocks and olefins and significantly improves the potential for the synthesis of chemicals from lignocellulosic biomass.