Effect of Zeolite Topology and Reactor Configuration on the Direct Conversion of CO₂ to Light Olefins and Aromatics

Abstract

The direct transformation of CO2 into high-value-added hydrocarbons (i.e., olefins and aromatics) has the potential to make a decisive impact in our society. However, despite the efforts of the scientific community, no direct synthetic route exists today to synthesize olefins and aromatics from CO2 with high productivities and low undesired CO selectivity. Herein, we report the combination of a series of catalysts comprising potassium superoxide doped iron oxide and a highly acidic zeolite (ZSM-5 and MOR) that directly convert CO2 to either light olefins (in MOR) or aromatics (in ZSM-5) with high space–time yields (STYC2‑C4= = 11.4 mmol·g–1·h–1; STYAROM = 9.2 mmol·g–1·h–1) at CO selectivities as low as 12.8% and a CO2 conversion of 49.8% (reaction conditions: T = 375 °C, P = 30 bar, H2/CO2 = 3, and 5000 mL·g–1·h–1). Comprehensive solid-state nuclear magnetic resonance characterization of the zeolite component reveals that the key for the low CO selectivity is the formation of surface formate species on the zeolite framework. The remarkable difference in selectivity between the two zeolites is further rationalized by first-principles simulations, which show a difference in reactivity for crucial carbenium ion intermediates in MOR and ZSM-5.

Selective methylation of toluene using CO 2 and H 2 to para -xylene

“…Recently, several types of oxide solid solution catalysts, such as ZnZrO x (ZZO), InZrO x , ZnAlO x , and ZnGaO x , have been investigated in CO 2 hydrogenated to methanol, olefins, or aromatics via the formate route with the methoxy intermediate (H 3 CO*) (12)(13)(14)(15)(16)(17)(18). In tandem catalysts composed of oxides and zeolites, intermediates can migrate between the two components (19)(20)(21)(22)(23)(24). Hydrogenation of CO 2 or CO can also directly produce aromatics (14-16, 22, 25, 26), but the production distribution is complex and the selectivity to xylene is usually less than 30%.…”

Coated sulfated zirconia/SAPO-34 for the direct conversion of CO2to light olefins

“…31 Note that due to the high content of K in the Fe based catalyst, mixed bed configurations result in the loss of acidity of the zeolite component. 14 The catalytic performance of the multifunctional systems is summarized in Fig. 4A.…”

“…In order to better understand the reaction mechanism we performed additional ssNMR characterization of samples after reaction, with special focus on characterizing organic species trapped in the zeolitic component. 14 In the 1D 1 H-13 C cross-polarization (CP) spectra (Fig. 5A), two primary features were clearly visible: (i) 10-30 ppm aliphatic/methyl groups, and (ii) 125-140 ppm olefinic/aromatic moieties.…”

“…9,10 In these bifunctional systems CO 2 conversion can proceed through two different routes depending on the first catalytic component: i) the transformation of CO 2 into methanol (MeOH) over a methanol synthesis catalyst 11 followed by a classical methanol to hydrocarbons (MTH) mechanism on the zeolite component 12 or, ii) the transformation of CO 2 into hydrocarbons via Fischer-Tropsch (FTS) over Fe based catalyst 13 followed by hydrocarbon oligomerization, cracking, isomerization and/or aromatization on the zeolite. 14 Nowadays, the MeOH route is most popular among researchers, as high selectivities to olefins among the total hydrocarbons can be achieved. 9,[15][16][17][18][19][20][21][22] Most of these works are built on the combination of Zr-based methanol catalysts with SAPO-34.…”

“…On the other hand, the FTS pathway has proven to be more productive and to lead to significantly lower selectivities to CO. 10,14 In this line, our group recently showed 14 that by combining an Fe catalyst with a MOR zeolite productivities of light olefins up to 9.2 mmol gcat −1 h −1 with a CO selectivity of 14% can be obtained at 375°C, 30 bars and 5000 ml h −1 gcat −1 (see Table S1 † for an overview of state of the art). However, in this case the product distribution is much wider, 14 with an important C 5+ fraction (resulting from the Fisher-Tropsch step) that is very difficult to convert into light olefins on the zeolite via cracking at the typical reaction temperatures. 3,23 Catalytic cracking of medium-range hydrocarbon fractions over solid acid zeolites is a well-known process, responsible for the manufacture of over 50% of gasoline in the world.…”