Zhibin Li

Synthesis of nano-SSZ-13 and its application in the reaction of methanol to olefins

Nanosized SSZ-13 has been obtained from a one-pot synthesis procedure with the addition of CTAB to the synthesis precursor solution. Nano-SSZ-13 zeolite showed high intracrystalline mesoporosity and compared to standard SSZ-13 presented a much longer lifetime and higher conversion capacity for the reaction of methanol to olefins. The improved properties were attributed to a more efficient utilization of micropores by easier diffusion of reactants and products and slower deactivation by coke. A higher C2/C3 ratio was found for nano-SSZ-13, pointing to a lower deactivation of the aromatics cycle of the hydrocarbon pool.

Effect of Ni doping in NixMn1−xTi10 (x = 0.1–0.5) on activity and SO2 resistance for NH3-SCR of NO studied with in situ DRIFTS

In this work, a series of NixMn1−xTi10 (x = 0.0–0.5) catalysts were synthesized using a one-pot sol–gel method for selective catalytic reduction (SCR) of NO with NH3. The effects of Ni doping on the catalytic activity and SO2 resistance were investigated by XRD, TEM-EDS, XPS, NH3-TPD, H2-TPR, SO2-TPD and in situ DRIFTS. It is found that the higher the amounts of surface Mn4+ and Oα species existing on the catalyst surface, the greater the oxidation ability that they present for NO and NH3, which results in better activity at low temperature and worse selectivity to N2 at high temperature due to the overoxidation of NH3. Among NixMn1−xTi10 (x = 0.0–0.5), the Ni0.4Mn0.6Ti10 catalyst exhibited excellent NH3-SCR activity, a wide temperature window (190–360 °C) and good H2O and SO2 durability even in the presence of 100 ppm SO2 and 15% H2O under a GHSV of 40 000 h−1, which is very competitive for the practical application in controlling the NOx emission from stationary sources. It is concluded that more surface Lewis acid sites and the appropriate contents of surface active Mn4+ and surface oxygen species on the surface of Ni0.4Mn0.6Ti10 play key roles in the special SCR performance due to the interactions among Mn, Ni and Ti oxides. The SO2-TPD and in situ DRIFTS results confirm the reason for the good SO2 resistance of the Ni0.4Mn0.6Ti10 catalyst. Moreover, in situ DRIFTS results reveal that the NH3-SCR reaction over Ni0.4Mn0.6Ti10 mainly follows the Eley–Rideal (E–R)-type mechanism.

Improving the catalytic performance of SAPO-18 for the methanol-to-olefins (MTO) reaction by controlling the Si distribution and crystal size

The physico-chemical properties of the small pore SAPO-18 zeotype have been controlled by properly selecting the organic molecules acting as organic structure directing agents (OSDAs). The two organic molecules selected to attempt the synthesis of the SAPO-18 materials were N,N-diisopropylethylamine (DIPEA) and N,N-dimethyl-3,5-dimethylpiperidinium (DMDMP). On the one hand, DIPEA allows small crystal sizes (0.1–0.3 μm) to be attained with limited silicon distributions when the silicon content in the synthesis gel is high (Si/TO2 ∼0.8). On the other hand, the use of DMDMP directs the formation of larger crystallites (0.9–1.0 μm) with excellent silicon distributions, even when the silicon content in the synthesis media is high (Si/TO2 ∼0.8). It is worth noting that this is the first description of the use of DMDMP as OSDA for the synthesis of the SAPO-18 material, revealing not only the excellent directing role of this OSDA in stabilizing the large cavities present in the SAPO-18 structure, but also its role in selectively placing the silicon atoms in isolated framework positions. The synthesized SAPO-18 materials have been characterized by different techniques, such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), N2 adsorption, solid state NMR, and ammonia temperature programmed desorption (NH3-TPD). Finally, their catalytic activity has been evaluated for the methanol-to-olefin (MTO) process at different reaction temperatures (350 and 400 °C), revealing that the SAPO-18 catalysts with optimized silicon distributions and crystal sizes show excellent catalytic properties for the MTO reaction. These optimized SAPO-18 materials present improved catalyst lifetimes compared to standard SAPO-34 and SSZ-39 catalysts, even when tested at low reaction temperatures (i.e. 350 °C).

Synthesis of MnNi–SAPO-34 by a one-pot hydrothermal method and its excellent performance for the selective catalytic reduction of NO by NH3

Mn- or/and Ni-modified SAPO-34 molecular sieves (Mn–SAPO-34, Ni–SAPO-34, and MnNi–SAPO-34) were synthesized by a one-pot hydrothermal synthesis method using morpholine as a structure directing agent. XRD, XRF, SEM, TEM-EDX, UV-vis-DRS, NH3-TPD, XPS, NMR, and in situ DRIFTS analyses were performed to study the properties of the samples. The MnNi–SAPO-34 catalyst demonstrated much better NOx conversion (>95%) and N2 selectivity (>98%) for the selective catalytic reduction (SCR) of NOx by NH3 than those of the other catalysts from 320 °C to 470 °C. Moreover, NOx conversion could still be maintained at about 100% at 380 °C even after 80 h over MnNi–SAPO-34. Its excellent activity can be ascribed to the strong interaction between the Mn and Ni species in the framework of MnNi–SAPO-34, leading to the suitable redox ability of MnNi–SAPO-34 by the reaction Ni3+ + Mn3+ ↔ Ni2+ + Mn4+. The in situ DRIFTS results suggested that the NH3-SCR reaction was mainly performed by an Eley–Rideal (E–R) reaction pathway at 300 °C for the MnNi–SAPO-34 catalyst. Thus, MnNi–SAPO-34 is considered as a promising candidate for controlling NOx emissions at middle temperatures.

Selective synthesis of the SAPO-5 and SAPO-34 mixed phases by controlling Si/Al ratio and their excellent catalytic methanol to olefins performance

The selective synthesis of SAPO-5, SAPO-5/SAPO-34 mixture and SAPO-34 was performed by increasing Si/Al ratio and pH through hydrothermal synthesis route, in which the product was successively switched from AFI to AFI/CHA and to CHA. The samples were characterized by XRD, XRF, SEM, and NH3-TPD techniques. It indicates that the SAPO-5/SAPO-34 mixture exhibits higher acidity than the pure SAPO-5 and SAPO-34 phases. During methanol-to-olefins reaction, the catalytic lifetime of the SAPO-5/SAPO-34 mixture was significantly longer than that of SAPO-34, which may be attributed to the moderate acidity of the SAPO-5/SAPO-34 mixture.