(264i) Design and Synthesis of Zeolite Catalyst for Production of Hydrocarbons from Methane Via Methanol
AIChE Annual Meeting
2022
2022 Annual Meeting
Materials Engineering and Sciences Division
Synthesis and Application of Inorganic Materials I: Synthesis
Tuesday, November 15, 2022 - 10:00am to 10:15am
Here, we report a novel catalytic process for selective and effective production of the hydrocarbons production from CH4 under mild conditions. Our strategy is that produced CH3OH from CH4 is immediately converted to hydrocarbons before over-oxidation of CH3OH; methanol to olefins (MTO) reaction involves in the MTM reaction. For this strategy, we have tackled the design and synthesis of zeolite catalyst that effectively catalyzes both MTM and MTO reactions under oxidizing atmosphere; both active sites for MTM and MTO reaction are created in single zeolite catalyst. Besides, in order to enhance the MTM reaction, oxidative conversion of CH4 was carried out in the presence of steam and highly active oxidant N2O.
In this sequential reaction, the adjacency between the active Cu site for MTM and acid site for MTO reactions would be important; acid sites should remain after the introduction of Cu species by ion-exchange method. Therefore, Al-rich aluminosilicate-type CHA zeolite (Si/Al atomic ratio = 3.8) was applied here. The H-form CHA (H/CHA) was prepared via typical procedure, and then Cu species were introduced into the zeolite by ion-exchange method (Cu-H/CHA). Note that Cu /Al ratio was low (ca. 0.04) to keep acid sites for the MTO reaction. As a control, Na-form CHA zeolite without acid sites (Na/CHA) was prepared and Cu-exchanged one was also prepared (Cu-Na/CHA). The XRD patterns of all the obtained samples showed a typical CHA-type structure. In addition, the XRD diffraction patterns of Cu-H/CHA and Cu-Na/CHA did not show any diffraction pattern originated from Cu species due to the high dispersion and/or small amount of Cu species (metal cation and oxides). The high dispersibility of the Cu species were also supported by their UV-vis. spectra.
Figure 1 shows the catalytic performance of Cu-H/CHA and Cu-Na/CHA, indicating that there were clear differences among the samples. Interestingly, both catalysts exhibited almost similar CH4 and N2O conversions along with time on stream (TOS). However, there was a marked difference in the productsâ distributions. Cu-H/CHA mainly produced CH3OH and hydrocarbons, while, for Cu-Na/CHA, the main product was CO2. As a control, the CHA zeolite without Cu and acidity (Na/CHA) did not show any catalytic performance (Figure S2). These results imply that the cooperative effect of Cu and H+ is crucial to the production of hydrocarbons, and that the formations of CO and CO2 are inhibited by the presence of acid sites. For Cu-H/CHA, the selectivity to CH3OH was decreased but that to hydrocarbons was increased along with TOS, suggesting that the CH4 is converted to the hydrocarbons via CH3OH and/or CH3OH derivates. This process of hydrocarbons production from CH3OH over zeolite catalyst is very similar to the MTO reaction. Regarding the distribution of the hydrocarbons produced, lower hydrocarbons such as C2-C4 were selectively produced. This is a typical feature of the MTO reaction over CHA-type zeolite; the hydrocarbon are produced by dissociation and desorption of the side chains of aromatic hydrocarbons formed by the âcarbon poolâ and/or âdual cycleâ mechanism.27, 54, 60 Hence, these results strongly suggest a new route to the production of the hydrocarbons from CH3OH, which is produced by oxidative conversion of CH4. Our findings will contribute to the effective utilization of CH4 as carbon resource, and to the development of a catalytic process for highly difficult and selective reaction.