Dft Study Of Dimethyl Ether Synthesis From Methanol On HZSM-5 Model Modification With Metal

With the rapid economic development and use of fossil fuel, environmental pollution has been one of the more severe problems. The shrinking of conventional primary energy needs to find an alternative and clean energy. And the dimethyl ether is a kind of ideal clean fuel. It is also a kind of important chemical raw materials, which can be used to produce other chemical products.Generally dimethyl ether is from methanol dehydration, and the modification of HZSM-5 catalyst for this reaction showed good catalytic performance. But the corresponding mechanism of dimethyl ether from methanol dehydration on the modification of HZSM-5 catalyst of is rarely involved.In the present work, we employ periodic DFT-GGA calculation method and double 5T cluster model. Based on the structure within the framework of two Al different distributions, Zd（two aluminum distance of 8.14 ?） and Zs（two aluminum distance of 4.84 ?） exist, respectively. Considering different distribution of two aluminums, reaction mechanism of dimethyl ether synthesis on the model with a variety of metals（Zn, Mg, Ca, Ga, Al, V and Zr） modified HZSM-5 is studied.The main conclusions of this work are summarized as follow:Single metal modified structure as [MZd] and [MZs], and two metal modified configuration for [MOM], the study of HZSM-5 zeolite modification with Zn²⁺, Mg²⁺, Ca²⁺ is found that :（1） catalytic activity in the same metal modification is [MZd]>[MZs], and activation energy on the [MOM] is slightlyhigher than on the [MZd];（2） comparing of the three metals modified HZSM-5on the reaction of dimethyl ether synthesis, HZSM-5 modification with Zn show better activity than the other;（3） path I of dimethyl ether synthesis from methanol is a possible path on Zn²⁺, Mg²⁺ and Ca²⁺ modified HZSM-5 model.One metal modified structure for [Zd-MO] and [Zs-MO], the study of HZSM-5 zeolite modifation with Ga³⁺, Al³⁺, Zr⁴⁺ and V⁴⁺ show that:（1） reaction on [Zd-MO] model show better activity than that on [Zs-MO] model, based on the same metal modification;（2） V modification structure [Zd-VO] has higher activity on dimethyl ether synthesis, the related activation energy of 0.82 eV;（3）in four kinds of metal modification reaction paths, the activation energy of path3(CH₃OH¹+Hâ†'CH₃O+H¹+H, CH₃OH+H+CH₃O+H¹â†'CH₃OCH³⁺H₂O+H¹) is lowest, so path 3 is the most possible reaction path.Comparing with the influence of methanol dehydration to form dimethyl ether on ZrOZn, ZrOAl, Zr OMg and Zr OGa models, it is found that:（1） the activation energy of dimethyl ether formation from methanol on four configurations were 1.09 eV, 0.89 eV, 0.93 eV and 0.90 eV, being helpful for dimethyl ether synthesis;（2） in three kinds of reaction path（path1, path2, path3）;path3 of methanol dehydration directly to form dimethyl ether, path 3(CH₃OH+CH₃OHâ†'CH₃O（H）CH³⁺OHâ†'CH₃OCH³⁺H₂O) of three possible path is the best path.