Preparation And Performance Study Of Methylcyclohexane Dehydrogenation Catalyst

With the rapid development of society,human beings are facing serious problems such as shortage of resources and increasing environmental pollution.Hydrogen energy,as a renewable energy with abundant reserves,has the advantages of high calorific value and no pollution,and is one of the most ideal clean energy sources at present.Due to the limitation of hydrogen storage and transportation technology,hydrogen energy is still not realized for large-scale industrial application.It is important to establish a safe and efficient hydrogen storage and transportation technology for the large-scale application of hydrogen energy.At present,the commonly used hydrogen storage technologies mainly include high-pressure gaseous hydrogen storage,low-temperature liquefaction hydrogen storage,adsorption hydrogen storage,metal hydride hydrogen storage,and organic liquid hydride hydrogen storage.Compared with other hydrogen storage technologies,organic liquid hydride hydrogen storage has many advantages,such as organic liquid hydride has higher hydrogen storage density,organic liquid hydride is liquid at room temperature,etc.,which greatly facilitates its storage and transportation.In this paper,the Ni-O-Al catalyst precursor was produced in one step by a modified co-precipitation method.The precursor of the catalyst was treated using evaporation of n-butanol,which effectively increased the specific surface area of the catalyst and the dispersion of the active component on the catalyst surface,in addition to the strong interaction between Ni and Al,which in turn inhibited the agglomeration of the active component Ni.A typical sample of Ni₂₀Al catalyst with moderate Ni content（20%）has a high specific surface area of 359 m²·g^-1.Through a series of characterizations,the results showed that the pretreated catalysts had smaller particles and higher dispersion of the Ni species and exhibited higher catalytic activity.Under the optimized conditions of T=450°C and LHSV=4m L·g^-1·h^-1,the conversion of methylcyclohexane reached 77.4%,toluene selectivity 85.6%and hydrogen release rate 63.94 mmol·g^-1·h^-1and the catalyst could be used stably for 29 h under the action of Ni₂₀Al catalyst.Although the catalyst prepared by the modified co-precipitation method exhibited good catalytic activity,the activity and stability of the catalyst were poor at low temperatures.Thus,this thesis continued to modify the Ni/Al₂O₃catalyst using Pt doping,and the results showed that the addition of Pt not only had a positive effect on the specific surface area of the catalyst(the specific surface area was increased to 453 m²·g^-1),but also could effectively reduce the average particle size of the metal Ni particles on the catalyst surface.In addition,the dehydrogenation performance of the methylcyclohexane dehydrogenation reaction was promoted due to the Pt-Ni bimetallic interactions,which could effectively improve the electronic structure of the metal Ni.At a reaction temperature of 350 °C,a catalyst dosage of0.6 g and a feed rate of 0.04 m L·min^-1,the conversion of methylcyclohexane reached 93.58%,the selectivity of toluene 87.49%,the hydrogen release rate 80.73 mmol·g^-1·h^-1 and the stable use time of the catalyst was increased from 29 h to 56 h.The addition of Pt has enhanced the activity and stability of the catalyst,but the selectivity of the target product still needs to be improved.In order to improve the selectivity of the target product and further extend the catalyst lifetime,Pt-Ni/Tix Al catalysts were prepared by Ti O₂ doping in this thesis,and the characterization results show that the introduction of appropriate amount of titanium can enhance the electron density above Ni and Pt and promote the hydrogen on the active component over the active component,in addition,the modification of Al₂O₃ by Ti O₂ reduced the density of weak acid sites and inhibited the demethylation of toluene and the generation of coke,and the introduction of titanium improved the mechanical strength of the catalyst,thus improving the catalyst lifetime.Under the optimal reaction conditions of 350 °C,0.6 g of catalyst and 0.08 m L·min^-1 of feed rate,the conversion of methylcyclohexane reached 99.71%,the selectivity of toluene 98.86%,the hydrogen release rate of methylcyclohexane 190.33 mmol·g^-1·h^-1,and the catalyst lifetime 71 h.