Characterization and Activity of Cr, Cu and Ga Modified ZSM-5 for Direct Conversion of Methane to Liquid Hydrocarbons

Direct conversion of methane using a metal-loaded ZSM-5 zeolite prepared viaacidic ion exchange was investigated to elucidate the roles of metal and acidity in the formation ofliquid hydrocarbons. ZSM-5 (SiO_2/Al_2O_3=30) was loaded with different metals (Cr, Cu and Ga)according to the acidic ion-exchange method to produce metal-loaded ZSM-5 zeolite catalysts. XRD,NMR, FT-IR and N_2 adsorption analyses indicated that Cr and Ga species managed to occupy thealuminum positions in the ZSM-5 framework. In addition, Cr species were deposited in the pores ofthe structure. However, Cu oxides were deposited on the surface and in the mesopores of the ZSM-5zeolite. An acidity study using TPD-NH_3, FT-IR, and IR-pyridine analyses revealed that the totalnumber of acid sites and the strengths of the Broensted and Lewis acid sites were significantlydifferent after the acidic ion exchange treatment. Cu loaded HZSM-5 is a potential catalyst fordirect conversion of methane to liquid hydrocarbons. The successful production of gasoline via thedirect conversion of methane depends on the amount of aluminum in the zeolite framework and thestrength of the Broensted acid sites.

Methane to Liquid Hydrocarbons over Tungsten-ZSM-5 and Tungsten Loaded Cu/ZSM-5 Catalysts

Metal containing ZSM-5 can produce higher hydrocarbons in methane oxidation. Many researchers have studied the applicability of HZSM-5 and modify ZSM-5 for methane conversion to liquid hydrocarbons, but their research results still lead to low conversion, low selectivity and low heat resistance. The modified HZSM-5, by loading with tungsten （W）, could enhance its heat resistant performance, and the high reaction temperature （800 ℃） did not lead to a loss of the W component by sublimation. The loading of HZSM-5 with tungsten and copper （Cu） resulted in an increment in the methane conversion as well as CO2 and C5＋ selectivities. In contrast, CO, C2-3 and H2O selectivities were reduced. The process of converting methane to liquid hydrocarbons （C5＋） was dependent on the metal surface area and the acidity of the zeolite. High methane conversion and C5＋ selectivity, and low H20 selectivity are obtained over W/3.0Cu/HZSM.

Optimization of methane conversion to liquid fuels over W-Cu/ZSM-5 catalysts by response surface methodology

The conversion of methane to liquid fuels is still in the development process. The modified HZSM-5 by loading with Tungsten （W） enhanced its heat resistant performance, and the high reaction temperature （800℃） did not lead to the loss of W component by sublimation. The loading of ZSM-5 with Tungsten and Copper （Cu） resulted in an increment in the methane conversion, CO2, and C5＋ selectivities. The high methane conversion and C5＋ selectivity, and low H2O selectivity are obtained by using W/3.0Cu/ZSM-5. The optimization of methane conversion over 3.0 W/3.0Cu/ZSM-5 under different temperature and oxygen concentration using response surface methodology （RSM） are studied. The optimum point for methane conversion is 19% when temperature is 753 ℃, and oxygen concentration is 12%. The highest C5＋ selectivity is 27% when temperature is 751 ℃. and oxwen concentration is 11%.