Xiaojun Bao

Stable and recyclable Pd catalyst supported on modified silica hollow microspheres with macroporous shells for enhanced catalytic hydrogenation of NBR

In this work, a stable and recyclable Pd catalyst supported on N-containing silane coupling agent modified silica hollow microspheres with macroporous shells (Pd/N-SHMs) was successfully prepared and used for the selective hydrogenation of nitrile-butadiene rubber (NBR) with enhanced catalytic performance. The results showed that Pd/N-SHMs possessed small-sized and well-dispersed Pd nanoparticles (NPs) and the macroporous shells were beneficial for the diffusion of macromolecular NBR, and thus with such a catalyst, the reaction could occur under mild conditions and high hydrogenation degree (96.6%) with 100% selectivity to C=C was obtained. The prepared catalyst could be easily recycled and reused with a high efficiency. More importantly, because of the strong coordination between Pd and diamine ligands, Pd NPs could be anchored steadily over the support and only 5.0xa0ppm Pd residues was detected in products. This reaction was considered as pseudo-first order at high H2 pressures, and the reaction activation energy was calculated to be as low as 18.1xa0kJ/mol. Our contribution is to provide an efficient and recyclable supported Pd catalyst, which may promote the development of heterogeneous catalytic systems for unsaturated macromolecular hydrogenation.

Tuning of the active phase structure and hydrofining performance of alumina-supported tri-metallic WMoNi catalysts via phosphorus incorporation

The effects of phosphorus on the structure and hydrofining performance of tri-metallic WMoNi/Al2O3 catalysts prepared with W/Mo-based hybrid precursor nanocrystals were investigated. The incorporation of phosphorus weakened the metal-support interactions (MSIs) and facilitated the formation of more synergetic NiWMoS phases with higher stacks. Catalytic tests using a fluid catalytic cracking diesel fuel showed that the changes in the MSIs and the morphology of the active phases had a more positive effect on the hydrodenitrogenation activity than on the hydrodesulfurization activity. In contrast, when phosphorus was incorporated into a tri-metallic WMoNiP/ Al2O3 catalyst prepared by a conventional incipient impregnation method, the MSIs decreased causing aggregation of the metal species which resulted in poorer hydrofining performance of the catalyst. These results show that incorporating phosphorus into a WMoNi/Al2O3 catalyst can finely tune the structure of the active phase to enhance the hydrogenation and hydrodenitrogenation activity of the resulting tri-metallic catalyst.

Dependence of Morphology, Dispersion and Hydrodesulfurization Performance of Active Phases in NiMo/SBA-15 on Loading Method

With the aim of exploring the dependence of morphology, dispersion and hydrodesulfurization (HDS) activity of active phases over SBA‐15 on loading method, four NiMo/SBA‐15 catalysts have been prepared by two different Mo introduction strategies with varying MoO3 contents (13 and 19u2005wt.% in each approach, respectively). One of the approaches is the conventional incipient wetness impregnation (IM) and the other is a new‐proposed Mo‐based inorganic‐organic hybrid nanocrystals as the precursor with hydrothermal‐assisted (HA) loading method. The results show that metal species are severely aggregated at a high concentration by IM method, leading to the poorly distributed MoS2 slabs with large sizes and ultra‐high stacking layers. While in case of the HA approach, the organic molecules surrounding the Mo species can isolate Mo species effectively to prevent them from aggregation and greatly improve the dispersion of active phases, even at high MoO3 loadings. Therefore, the HDS activity is improved as increasing the amounts of MoO3 for the catalyst prepared with HA method because of the more active sites accessible to the reactants, however, HDS activity is decreased for the catalyst acquired by the IM method due to the serious metal aggregation. It is demonstrated that the HA method is favorable for the better dispersion of active phases over SBA‐15 with the help of organic molecules leading to the effective MoS2 morphology with remarkably enhanced catalytic activity, and such superiority of the HA approach is more prominent at high MoO3 loadings.

Synthesis of Pd/SiO2 Catalysts in Various HCl Concentrations for Selective NBR Hydrogenation: Effects of H+ and Cl– Concentrations and Electrostatic Interactions

A series of silica supported Pd (Pd/SiO2) catalysts were prepared in various HCl concentrations (CHCl) of the impregnation solution with different electrostatic interactions between Pd precursor and support, and their catalytic properties were evaluated by the selective hydrogenation of nitrile butadiene rubber (NBR). The results show that with the CHCl increasing from 0.1 to 5 M, the particle size of Pd nanoparticles dramatically decreases from 24.2 to 5.1 nm and stabilizes at ∼5 nm when CHCl is higher than 2 M. Using the catalysts prepared with a high CHCl (>2 M), an excellent hydrogenation degree (HD) of ∼94% with 100% selectivity to C=C can be acquired under mild conditions. Interestingly, the HD could be remarkably increased from 65 to 92% by increasing only CCl– from 0.1 to 2 M with the addition of NaCl while keeping CH+ at 0.1 M. This is because PdCl42– is the predominant existing form of precursor at high CCl–, which has a strong electrostatic attraction with the positively charged support favorable for the formation of small-sized Pd nanoparticles over silica. Notably, Pd leaching behavior during the hydrogenation reaction is closely related to CH+, and the higher the CH+, the less Pd residues are detected in the hydrogenated NBR. Our contribution is to provide a facile strategy to synthesize effective and stable Pd/SiO2 catalysts via adjusting the electrostatic interaction, which exhibits a high activity and selectivity for NBR hydrogenation.

Carboxylic acids to butyl esters over dealuminated–realuminated beta zeolites for removing organic acids from bio-oils

This article describes a novel method to dealuminate and realuminate H-beta zeolites as catalysts for removing organic acids from bio-oils via their esterification reactions with alcohols. Modified H-beta zeolites were prepared by leaching with solutions of oxalic acid, DL-malic acid, and DL-tartaric acid that have different numbers of hydroxyl groups. The results showed that, while all three organic acids can dealuminate the parent H-beta zeolite, with Al(VI)a atoms and Al(IV)c ones being preferentially removed, they show quite different realumination abilities, with tartaric acid with two hydroxyl groups having the highest realumination ability. The concomitance of dealumination and realumination and their dependence on the hydroxyl group numbers of the organic acids provide the possibility of finely tuning the Al and acidity distributions of the resulting zeolites. Among the three acid treated H-beta zeolites, the one obtained from malic acid leaching exhibited the best performance in catalyzing the esterification reaction between acetic acid and sec-butyl alcohol, attributed to its suitable quantity and density of medium and strong Bronsted acid sites and enhanced aluminum gradient. The catalytic results obtained in a fixed-bed microreactor revealed that the malic acid leached H-beta exhibited dramatically enhanced catalytic performance compared to the commercial ion-exchange resin Amberlyst® 15, demonstrating great potential for industrial application.