•A statistical analysis was put forward to determine the preferred T sites and the proton siting of zeolites.•The degree of freedom and the k-point mesh in calculation have key influences on the energy and vibrations of zeolites.•The tradeoff between the calculation precision and the costs leads to a better choice of a practical methodology.Various models have been utilized to investigate the Brönsted acidity (BA) of zeolites which affects the acid strength and the catalytic performance of zeolite catalysts. They sometimes yield confusing results in literature. To understand this phenomenon, the zeolite ferrierite as a typical example was investigated in this study by using calculation parameters similar to, if not more accurate than, the previous ones. The tradeoff between the calculation precision and the costs indicates that relaxing all atomic coordinates through lower k-point meshes would be a better choice to study the acidic ferrierite. Our results demonstrated that it would be better to determine the preferred T sites for the Al substitution and the proton siting of zeolites in a statistical view. This study is expected to shed light on the methodology validity in the practical application to solve the acidic zeolites.Zeolites are large-scale molecular structures in three-dimensional networks of pores and cages. What about the tradeoff between the efficiency and the precision when some approximations are employed? It is challenge to finger out which the preferential T atom is and where the proton siting is because of the relative narrow RSE or RPDE range, the uneven T sites, and the ubiquitous computational error. A statistical analysis was put forward in this study.

•Hierarchical nano-ferrierite aggregates were synthesized using pyrrolidine as the sole OSDA.•Hierarchical nano-ferrierite aggregates consisted of mainly intercrystalline mesopore due to the stacking and assembly of nano-particles.•The size of nano-ferrierite was in the range of 40–180 nm depending on the crystallization temperature and initial gel compositions.•Excellent catalytic stability and product selectivity in 1-butene skeletal isomerization reaction were observed.Nano-ferrierite zeolite aggregates with hierarchical porosity were successfully prepared by using pyrrolidine as sole organic structure-directing agent. SEM and TEM images revealed that nano-sized crystals (40–60 nm) stacked together loosely to form irregular clusters. Influence of crystallization temperature and initial gel compositions (pyrrolidine content, alkalinity, water content) on the synthesis of ferrierite zeolite were investigated in detail. Low crystallization temperature and high alkalinity were beneficial to form nano-ferrierite zeolite aggregates with high hierarchical porosity (total pore volume: 0.461 cm3/g). Compared with commercialized ferrierite zeolite, hierarchical nano-ferrierite aggregates showed better catalytic stability and product selectivity in the 1-butene skeletal isomerization reaction.Download high-res image (196KB)Download full-size image

A series of ZSM-35 zeolites with different alkaline treatment degrees were prepared. The precise effects of alkaline treatment on composition, morphology, porosity, transportation and acidity of the samples were characterized by means of multiple techniques including N2 sorption, transmission electron microscopy (TEM), intelligent gravimetric analyzer (IGA) and Fourier transform infrared spectroscopy (FTIR). ZSM-35 after moderate alkaline treatment exhibited enhanced carbonylation activity compared with the parent sample. As revealed by the N2 adsorption and TEM results, alkaline treatment could induce the deaggregation of ZSM-35 clusters and remove the amorphous debris on the surface of ZSM-35 platelets. Furthermore, an improved diffusion behavior of the dimethyl ether reactant molecule was observed on the alkali-treated sample from IGA experiments which directly led to the better catalytic performance for the carbonylation of the dimethyl ether with carbon monoxide. Mesoporosity created by severe alkaline leaching does not enhance the catalytic properties of ZSM-35 in dimethyl ether carbonylation reaction. Especially, a decrease in reaction stability was observed due to the limitation effect of carbonaceous deposit formation.

A series of Mo/mordenite-alumina catalysts with progressive sodium exchange degrees in mordenite were prepared and their performance in 1-butene metathesis reaction was evaluated. Significant variations in product distribution and catalytic activity were observed when the exchange degree of mordenite changed. As revealed by NH3-TPD and 1H MAS NMR results, the acid site density and distribution over the catalysts were directly related to the degree of ion-exchange of sodium in mordenite. The change of support acidity led to different anchoring modes and dispersion of Mo species on the support which further resulted in the different reduction behavior of Mo species under olefin atmosphere. A good correlation between product distribution and properties of the catalysts was proposed.Graphical abstractHighlights► 1-Butene metathesis product distribution could be tuned through changing the sodium exchange degree of mordenite. ► 1-Butene self-metathesis dominates on the catalyst with low sodium exchange degree due to the limitation of 1-butene isomerization. ► High propene yield of 27.4 mol% is obtained on 6Mo/HMOR–Al2O3. ► Anchoring modes and dispersion of Mo species are closely related to the sodium exchange degrees of the support.

Influences of alkaline treatment on the structural properties and catalytic performances of ZSM-5/ZSM-11 composite zeolites with alumina as binder at different preparation steps were studied in the present investigation. Temperature-programmed desorption of ammonium (NH3-TPD) and pyridine infrared (Py-IR) spectra revealed that alkaline treatment sequences changed both the distribution and amount of the acidities in the ZSM-5/ZSM-11-Al2O3 samples. The mesopores created by alkaline treatment were found beneficial for the diffusion of aromatic molecules, as determined by the xylene-uptake experiments using a tapered element oscillating microbalance (TEOM). In 1-hexene isomerization and aromatization reactions, the sample after extrusion followed by alkaline treatment exhibited excellent aromatization activity and stability compared with other samples undergoing different treatment sequences. The enhanced catalytic performance could be attributed to the redistribution of acid sites and introduction of more mesopores.Graphical abstractS2 sample prepared by ZSM-5/ZSM-11 extrudate with successive alkaline treatment showed enhanced mass transfer performance for aromatic molecules as verified by the m-xylene uptake experiments.Research highlights▶ Influences of alkaline treatment on the structural properties and catalytic performances of ZSM-5/ZSM-11 composite zeolites with alumina as binder at different preparation steps were studied. ▶ ZSM-5/ZSM-11-Al2O3 catalyst for 1-hexene isomerization and aromatization reaction. ▶ ZSM-5/ZSM-11 after extrusion followed by alkaline treatment exhibited best catalytic performance among four samples. ▶ Better mass transfer performance for aromatic molecules in sample S2 was verified by the m-xylene uptake experiments using tapered element oscillating microbalance (TEOM).

•Ion exchange method is beneficial for the formation of ZnOZn bridging species inside the micropore channel.•ZnOZn bridging species increase the promoting effect of cofeeding n-butane with methanol on aromatics selectivity.•Bulk ZnO particles promote the formation of C2 C4 light alkane in cofeeding reaction.Combination of the exothermic methanol aromatization with the endothermic n-butane aromatization provides a good way to meet the increasing demand for aromatics. Here, a series of Zn-ZSM-5/ZSM-11 catalysts were prepared with different introduction methods. The influence of location and state of Zn species on the coupling effects of cofeeding n-butane with methanol were investigated in detail. UV–vis, H2-TPR and XPS spectra were applied to reveal the state of the Zn species on different catalysts. Quantitative results of NH3-TPD and Pyridine-FTIR were provided to compare the acidity changes of the catalyst after Zn loading. Physical mixing method led to high portion of bulk ZnO particles outside the channel which could promote the formation of C2 C4 light alkane in cofeeding reaction. Ion exchange and impregnation modes were beneficial for the formation of ZnOZn bridging species in the micropore channel. ZnOZn bridging species was found to increase the promoting effect of cofeeding n-butane with methanol on aromatics selectivity.Download high-res image (196KB)Download full-size image