Promoting hexane activation to further improve propylene selectivity has been a challenge. In this study, the activation mechanisms of hexane on Br & oslash;nsted acid sites (BAS) of ZSM-5, on metal-doped Lewis acid sites (LAS) and on mixed systems with olefins have been investigated by density functional theory (DFT), microkinetics and experiments. DFT results show strong BAS are more favorable for the activation of hexane compared to weak BAS. The existence of two mechanisms for the activation of hexane under LAS. The activation of hexane to generate hexene and hydrogen on the LAS under M-I type metal doping, Ni and Cu belong to the M-I type metals, where Ni metal promotes C-H bond breaking more effectively (136.11 kJ/mol). On the other hand, under M-II type metal doping, the activation of hexane to produce hexyl carbenium ions, Co, Mn, Fe, and Zn belong to the M-II type metals, with Co metal exhibiting the highest efficiency in promoting C-H bond cleavage (18.56 kJ/mol). Among the mixed systems of olefin and hexane, the mixed system of pentene and hexane was chosen to be more effective. Microkinetics revealed that reactions occurred at lower temperatures on LAS compared to BAS. Furthermore, the capability to promote hexane activation was ranked as follows: LAS>olefin addition > BAS, which is consistent with the experimental results. To further promote hexane activation, it is necessary to dope the catalyst with Co metals and reduce the reaction temperature appropriately. Additionally, a small amount of olefin can be added in the process. This study provides a theoretical basis for the design of catalysts and optimization of operation conditions.

The reason for high-difficulty nitrogen removal of aromatic N-heterocyclic compounds in petroleum fractions was investigated from the main thought of "NiWS property - Reaction behavior - DFT calculation". The properties of the used catalyst were characterized by a series of techniques with the aim of providing the basis for model construction in the DFT calculations. The kinetic experiments in fixed-bed reactor revealed that although 1,2,3,4tetrahydroquinoline (THQ1) and decahydroquinoline (DHQ), o-ethylaniline (OEA) exhibited relatively high yields in the HDN reaction of quinoline and indole respectively, they were all able to show high conversions and HDN rates when reacted as feedstocks alone. The study of product normalizations in the reaction system of the mixed feedstocks demonstrated that the difficulty of conversion of THQ1 and DHQ in quinoline HDN was mainly due to the inhibition effect of quinoline feedstock. While in the HDN of indole, the presence of the intermediate product OEA was the main factor for the low conversion of indole. This phenomenon of inhibition originating from within the molecular reaction network was proposed as N-N self-inhibition effect for the first time. The DFT calculations suggested that the inhibition of quinoline on THQ1 could be attributed to the adsorption advantage of quinoline, while the inhibition on DHQ was mainly due to the steric hindrance effect of DHQ itself. And the inhibition effect of OEA on indole can be mainly attributed to its greater nucleophilicity and stronger adsorption ability on the active sites compared with IND.

It has been a challenge to accurately control the monomolecular pathways, bimolecular pathways and aromatization reactions in the catalytic pyrolysis of naphtha to further improve the selectivity of propylene. The dynamic variations of intermediate species in these three pathways were simulated using microkinetics under a wide range of operating conditions. The intermediate species in the active site and the rate controlling step as a function of temperature were identified. The optimum temperatures for the monomolecular, bimolecular and aromatization pathways were determined to be 1000 K, 950 K and 1200 K, respectively. Meanwhile, it is confirmed that most of the propylene originate from the bimolecular pathways. The results of the microkinetics were verified by DFT studies and experiments. The DFT results show that C5 and C6 carbeniums ions are more likely to occupy the active site for reaction. In the experiment, with increasing temperature, the proportion of the monomolecular pathways initially decreased and then increased, while the bimolecular pathways changes in the opposite direction. In addition, pressure affected the optimal temperatures but had insignificant impact on the maximum reaction rate and product selectivity for the three paths. As for the catalytic pyrolysis reaction of hexane, it is suggested that the optimal temperature and pressure be set at 950 K and 101.32 kPa, which promoted the occurrence of the main reaction path and inhibits the aromatization reaction, while maximized the selectivity of propylene. This study provides new insights into the control of the reaction pathway and optimization of operating conditions for the catalytic pyrolysis of n-hexane to produce propylene.

It is a challenge to effectively control the intermediate ring hydrogenation products in tricyclic aromatic hydrocracking reactions in order to further increase the selectivity of BTX. A series of doped gallium modified CoMo/Al2O3 catalysts were prepared, the effect of gallium on the catalyst's physicochemical properties, active phase structure and hydrogenation reaction pathway was studied. The study revealed that the doping of gallium species promoted the sulfidation of Mo species and improved the catalytic activity of the catalyst. The 1% Ga-modified catalyst showed the best selective hydrogenation performance, in which the conversion rate of phenanthrene was up to 83.75% and the selectivity for dihydrophenanthrene reached 28.60%. In addition, DFT calculations show that the introduction of Ga into the active phase between the Co and Mo atoms results in a higher differential charge density in the middle ring, which is more conducive to hydrogen adsorption.

Acid strength is an important factor affecting the reaction mechanism. The influences of different Brønsted acid strengths on the cracking path of n-hexane were systematically investigated using the density functional theory. Most of the hexane activation cracking transition states are carbenium ions with no intermediate products of five-coordinate hexanium due to the weak Brønsted acid sites were not conducive to the stabilization of hexanium ions. With increasing acid strength, the protonated cracking reaction (the rate-controlling steps of monomolecular paths) energy barrier was reduced by 38.0% and the β-scission reaction (the rate-controlling steps of bimolecular paths) energy barrier was reduced by 27.15%, where enhanced the selectivity of E&P by changing the ratio of monomolecular and bimolecular cracking. However, the optimal reaction paths, the rate-controlling steps and the order of the various reaction energy barriers haven’t been changed. In addition, decreasing the acid strength increased the energy barriers of aromatization reaction and inhibited the reaction. The effect of molecular size on aromatization was further explored. The intermolecular hydrogen transfer reaction between 2-propoxide and 3-ethylcyclohexene is the rate controlling step and the larger the cycloalkane molecule, the higher the reaction energy barrier. The catalyst design requires a reduced pore size to prevent the formation of cycloalkanes and thus inhibit side reactions to improve the selectivity of E&P.

Herein, the effect of in-situ Ti modification on the physicochemical properties of the TixY zeolites and the corresponding NiW supported TixY-A catalysts, as well as on the catalytic performances for aromatic N-het-erocyclic compounds hydrodenitrogenation (HDN) was investigated. The existing forms of Ti atoms in the Y zeolites and the active metal states of the corresponding catalysts were investigated by XRD, ICP-OES, SEM, FTIR, UV-Vis DRS, CP-MAS NMR, N2 physical adsorption-desorption, Py-FTIR, H2-TPR, HRTEM, XPS and DFT calculation. The results show that the Ti atoms can be effectively introduced into the Y zeolite framework by the in-situ hydrothermal crystallization method. With the increase of TiO2/Al2O3 molar ratio in the Y zeolite, the amount of Bronsted acid sites of the zeolite tended to decrease constantly, but the reducibility of the catalyst and the stacking layer number as well as the sulfidation degree of the NiWS active phase continued to be enhanced. The highest quinoline and indole conversions of 86.5 % and 46.9 % at 320 degrees C, 4.0 MPa, 300 H2/oil (v/v), and 10 h-1 LHSV, as well as the highest TOFs of 2.24 h-1 and 1.04 h-1, the highest kHDN values of 12.4 x 10-4 mol center dot g- 1 center dot h-1 and 3.6 x 10-4 mol center dot g- 1 center dot h-1, and the highest denitrogenated product selectivities of 46.1 % and 66.2 % under quinoline and indole conversions of about 15 % and 50 % respectively have been achieved in catalyst NiW/Ti0.1Y-A due to the perfect matching of its hydrogenation and hydrogenolysis performance, which was mainly derived from the remarkable synergistic effect between the Bronsted acid sites of the Y zeolite and the NiWS active phase of the catalyst.

Catalytic pyrolysis is an important way of integrating refining and petrochemical processes, as it efficiently converts FCC gasoline into propylene. Enhancing the selectivity of propylene production remains a major focus in this field. To enhance the selectivity of propylene in catalytic pyrolysis of olefin, the reaction mechanism, the microkinetics of the catalytic pyrolysis of 1-hexene, as well as the effect of acid strength were investigated using the density functional theory. The optimal paths to light olefins are determined, in which beta-scission reaction is the rate controlling step to produce propylene in 1-hexene cracking paths. Meanwhile, increasing the acid strength will reduce the apparent activation energy of the reaction and facilitate the path to propylene production than the path to ethylene production. The microkinetic modeling shows that the system rate controlling step gradually shifts from a high-energy-barrier reaction to an adsorption reaction of reactants as the reaction temperature increases. In addition, the proportion of monomolecular mechanisms is larger than the bimolecular mechanism under high temperature conditions and the yield of propylene reaches maximum at 750 K, which helps optimize operating temperature for catalytic pyrolysis of 1-hexene. The work can offer new insights into the mechanism of catalytic pyrolysis of olefins and provide a theoretical guide for designing highly active catalysts for such reactions.

A series of SAPO-11 molecular sieves were synthesized in the concentrated gel system by reducing the water content in the synthesis system. With SAPO-11 molecular sieves as supports, NiW-supported catalysts were prepared for the hydroisomerization of n-hexadecane. SAPO-11 molecular sieves and catalysts were characterized by XRD, SEM, N-2 adsorption-desorption, NH3-TPD, Py-IR, HRTEM and XPS. The results showed that reducing the water content in the synthesis system could increase the mesoporous volume of SAPO-11 molecular sieve and improve the acidity of SAPO-11. For the corresponding catalysts, using SAPO-11 synthesized in concentrated gel system as the support weakened the interaction between the active phase and the support, and increased the dispersion and stacking number of the active phase, which effectively improved the catalytic performance of the catalyst. The yield of i-hexadecane of the catalyst NiW/45W-SA corresponding to SAPO-11 synthesized in conventional water content system was 28.14%, while that of the catalyst NiW/5W-SA corresponding to SAPO-11 synthesized in concentrated gel system was 52.24%. According to the distribution of isomers, it is inferred that hydroisomerization of n-hexadecane over NiW/SAPO-11 follows the pore-mouth mechanism.

In this study, the mechanism and microkinetics of 1-butenecatalytic cracking were investigated. Based on the calculation results of thefull reaction, the optimal paths for 1-butene isomerization anddimerization-cracking were clarified, and a new aromatization mechanismis proposed. In addition, the effect of reaction temperature variation onthe product distribution was clarified. Limited by the amount of 1-buteneadsorbed, increasing the temperature will gradually change the rate-determining step of the system and have negative effects on the reactionrate. In the temperature range suitable for the production of ethylene andpropylene, this effect becomes very significant. Therefore, appropriatelyincreasing the number of Bronsted acid sites in the catalyst to ensure highadsorption amount of 1-butene at high temperatures is an effective way toimprove the production of ethylene and propylene in catalytic cracking ofbutene

This paper mainly studies the travel time impedance functions of urban transportation networks including two parts: the uninterrupted flow function and interrupted flow function. On the basis of uninterrupted flow’s speed-flow relationship, we propose a piecewise method to research on its impedance function. In the interrupted flow function, links and intersections are considered separately. Each kind of turn delay at signal intersections is estimated through the delay function of HCM2000. The impedance functions are used in a macroscopic simulation model to prove the feasibility in practice.