Silicone rubber foam was prepared by direct rapid depressurization foaming process using supercritical CO 2 as foaming agent. It was found that under high temperature and pressure, the dissolution of CO 2 and the vulcanization reaction occurred simultaneously. The vulcanization degree range with good cell morphology was between 19.8% and 48.2%. When the saturation pressure exceeded 16 MPa, the cell morphology did not depend on foaming pressure. When the temperature was increased from 110 °C to 140 °C, the degree of vulcanization increased from 1.8% to 60.5%, and the cell size ranged from 13.9 µm to 646.4 µm, with an order of magnitude variation in cell density. This study identified the key control factors for supercritical CO 2 relief foaming of silicone rubber and provided a fast and efficient preparation method, as well as theoretical guidance, for obtaining lightweight microporous silicone rubber foams.
Xiaotong Meng,Yuchao Lyu,Junhao Liu,Wenshuo Ma,Yupeng Tian,Jianye Fu,Xinmei Liu
Spent catalysts from the hydrofining process are hazardous wastes, while their appropriate utilization can also bring enormous environmental and economic benefits. Herein, a chemical resurrection method was developed to resurrect and recycle the industrial spent NiMo/Al 2 O 3 hydrofining catalyst. The spent catalysts are calcined to remove the carbon deposit followed by the treatment with citric acid (CA) and ethylene glycol (EG). The results show that the calcination can also accelerate the aggregation and inerting of the active phase. However, the redispersion and reactivation of the inactive phases over the spent catalysts are realized through formation of metal complex with the citric acid, which weaken the interaction between Mo species and support. It increases reducibility of the Mo species and then improve the sulfurization degree of the resurrected catalyst. Besides, the average length of MoS 2 is reduced while the stacking number is increased. The ethylene glycol further regulates the reducibility of Ni and Mo species to promote the formation of NiMoS phase with high activity instead of Ni 3 S 2 . Consequently, the average length of the MoS 2 is reduced while the average stacking number of MoS 2 and content of the NiMoS phase are increased over the resurrected catalyst compared with the spent catalyst. It recovers the hydrodesulfurization activity of the resurrected catalyst to a level higher than that over the spent and industrially regenerated catalyst.
Regulation of electronic structure of metal active phase for catalysts has been known as efficient in promoting its catalytic activity; however, manipulating the activity of catalysts via controllable metal active phase electronic structure is still challenging. A non-equilibrium electronic structure Fe-based bulk catalyst has been developed via controllably adding P species, where the non-equilibrium electronic structure of Fe species is formed through the electron transfer from the Zn species through the P electronic channel. As a result, the catalytic activity of the modified Fe-based bulk catalysts has increased by 24.4–50.4%. Meanwhile, the sulfurization degree (SD) of the modified Fe-based bulk catalysts has increased by 5.6–25.9%. In addition, the HDS reaction rate constant ( k HDS ) has increased by about 2.0 times, and the DDS reaction rate constant ( k DDS ) has increased by about 2.4 times. The P modifying can regulate the directional transfer of unpaired free electrons between Fe and Zn species to form a more non-equilibrium electronic structure of Fe species, which can reduce the energy barrier of the C–S bond adsorbed on the P-modified Fe-based bulk catalysts. Importantly, the P species can be used as an active site to adsorb S-containing compounds in the modified Fe-based bulk catalysts, which is conducive to generating more coordinatively unsaturated sites (CUSs). The former can promote the formation of the more non-equilibrium electronic structure of Fe species, and the latter can adjust the adsorption active site of S-containing on the catalyst surface. Therefore, an electron transfer channel is formed among Fe, Zn, and P species, and another one is formed among Fe, P, and S-containing compounds, which form a dual-channel electron transfer behavior. Furthermore, the specific surface area, total pore volume, and reducibility of the modified Fe-based bulk catalysts have also shown varying degrees of improvement via the controllable addition of P species.
危险品化学品经营许可证（带存储）