Preparation And Physicochemical Properties Regulation Of Mesoporous Tobermorite Catalysts

The inorganic layered catalyst exhibits high activity and strong selection function in the field of macromolecular catalytic reaction due to its open layer structure.It is usually modified by swelling,pillaring,stripping and inter-layer reaming.However,the existing modification measures have the problems of desiliconization and dealuminization,which cause the catalyst skeleton to be destroyed,and the organic template is required to be used and the modification process is complicated.Not conducive to green manufacturing.The unique 11?layer spacing of tobermorite provides a suitable channel for macromolecular diffusion.Calcium ions and water molecules between the tobermorite layers and silanol groups on the silicon chain provide a rich acid-base active center.At the same time,the loose intergranular structure of the crystals can also allow the formation of defects by means of isomorphous replacement to modulate the acidity and alkalinity.First,the dynamic hydrothermal synthesis method wa s used to systematically investigate the effects of various water-solid ratios,reaction time,molar ratio of Ca/Si,and the type of silicon source on the physicochemical properties of tobermorite.The composition,micromorphology,specific surface area and pore structure of tobermorite were analyzed by XRD,SEM,BET,NH₃-TPD and CO₂-TPD.The results show that using the silicon micropowder as the silicon source and the calcium hydroxide as the calcium source,the suitable synthesis condition of layered tobermorite crystal is Ca/Si molar ratio of 0.83,the water-solid ratio of 20,180°C hydrothermal reaction for 10 h.The layered tobermorite catalyst was mainly composed of weak acid-base active center,the specific surface area was 65 m²?g^-1,the pore volume was 0.15 cm³?g^-1,and the total acid amount and total alkali amount were0.181 mmol?g^-1 and 0.467 mmol?g^-1,respectively.When used fumed silica&silica micropowder as the blending silicon source,the specific surface area of the tobermorite can be controlled in the range of 65²20 m²?g^-1,the pore volume can be adjusted in the range of 0.15⁰.71 cm³?g^-1,the total acid amount can be regulated in the range of 0.127⁰.181 mmol?g^-1,the total alkali amount can adjusted in the range of 0.365⁰.467 mmol?g^-1,and the pore size of mesoporous tobermorite was concentrated at 3³3nm.The effects of various aluminum sources and doping amounts on the physicochemical properties of aluminum-doped mesoporous tobermorite were investigated by the principle of isomorphous substitution.The catalytic performance of aluminum-doped mesoporous tobermorite catalyst in the synthesis of methyl mercaptan by hydrogen sulfide methanol method was investigated.The crystal structure,micromorphology,pore structure,thermal stability and acidity and alkalinity of tobermorite were analyzed by XRD,SEM,XRF,XPS,FTIR,BET,NH₃/CO₂-TPD and TG.The results show that various aluminum sources have a great influence on the crystal phase composition of the synthesized products.It is successful to carry out isomorphous substitution modification of tobermorite with pseudo-boehmite as aluminum source.The thermal decomposition temperature of aluminum-doped tobermorite crystals increased by about 10°C,the mesoporous pore size was concentrated at 3¹8 nm.The active sites of strong acid and strong base appeared in the aluminum-doped tobermorite crystal,but the total acid amount and total alkali amount of it decreased to 0.122 mmol?g^-1 and 0.374 mmol?g^-1,respectively.Under the reaction conditions of pressure of 1.0 Mpa,temperature of 370°C,H₂S/CH₃OH molar ratio of 2:1,N₂ flow rate of 90 mL?min^-1,the CH₃OH conversion,CH₃SH selectivity and CH₃SH yield of the aluminum-substituted tobermorite catalyst?the amount of aluminum substitution is 11.7%?were 55.39%,80.82%and 44.77%,respectively.Based on the principle of isomorphous substitution,the effects of phosphorus doping into the mesoporous tobermorite structure on its crystal structure,pore structure,thermal stability and acidity and alkalinity were investigated.The catalytic performance of phosphorus-doped mesoporous tobermorite catalyst in the synthesis of methyl mercaptan by hydrogen sulfide methanol method was investigated.The results show that the specific surface area and pore volume of phosphorus-doped tobermorite crystals increase to 232 m²?g^-1 and 0.95 cm³?g^-1,respectively.The pore size of mesoporous tobermorite is concentrated in 3¹8 nm,and the total acid amount and total alkali amount decreased to 0.144 mmol?g^-1 and 0.390mmol?g^-1,respectively.The CH₃OH conversion,CH₃SH selectivity and CH₃SH yield of the phosphorus-substitution tobermorite catalyst?the amount of phosphorus substitution is 6.1%?were 56.77%,75.09%and 42.63%,respectively.