Design and Synthesis of Bioinspired ZnZrO_x&Bio-ZSM-5 Integrated Nanocatalysts to Boost CO₂ Hydrogenation to Light Olefins

Abstract

Transformation of CO 2 with the help of green hydrogen (prepared from renewable energy) into valuable light olefins (C 2 = −C 4 =) is a promising route for utilizing the carbon resource in CO 2 . Currently, most of the reported bifunctional catalysts for CO 2 hydrogenation to light olefins follow a methanol-mediated route that adopts SAPO-34 as the zeolite component. Although ZSM-5 has been widely used in the methanol to propylene process using fixed bed reactors due to high shape-selective property and long lifetime, ZSM-5-based bifunctional catalysts have seldomly been used for CO 2 hydrogenation to light olefins. Herein, we proposed a novel synthetic strategy for bio-ZSM-5 with mild acid strength and relatively low acid density using the natural rice husk as a template. The bio-ZSM-5 was integrated with ZnZrO x solid solution nanoparticles, and the derived ZnZrO x &bio-ZSM-5 catalysts exhibited a high C 2 = −C 4 = selectivity of 64.4% and total C 2 −C 4 selectivity of 94.5%, but relatively low CH 4 selectivity (5.5%) and aromatic selectivity (<1%). The post-modified ZnZrO x &bio-ZSM-5 catalysts further enhanced the catalytic stability with less coke deposition and regulated the ethylene to propylene ratio in light olefin distribution. Furthermore, *CH x O was found to be the key intermediate formed on the ZnZrO x surface and was transferred to the Brønsted acid sites in the bio-ZSM-5 for the subsequent conversion to light olefins, as confirmed by in situ DRIFTS and chemical trapping mass spectrometry.

Light olefin synthesis from a diversity of renewable and fossil feedstocks: state-of the-art and outlook

“…Using, for example, ball milling could be excessive and may affect negatively the performance. 407 Recently, In- and Zn-species were shown to be mobile under the LO synthesis reaction conditions and can block the Brønsted acid sites and hence, destroy the catalyst bifunctionality. 426 Such processes can be intensified due to the smaller distance between the components and reduce the activity and selectivity of the catalysts.…”

“…399 For the In 2 O 3 –ZnZrO x /SAPO-34, the CO 2 conversion remained constant as well as LO selectivity for at least 92 h. 423 The similar trend was observed over other catalysts, which worked without noticeable conversion and selectivity changes for a long period of time. 388,407,416,417,430…”

“…Reprinted (adapted) with permission from ref. 407 Copyright 2021 American Chemical Society. (c) Preparation of the core-shell ZnCrO x @SAPO-34 catalyst.…”

“…Biomass-derived hierarchical ZSM-5 may provide a B65% CO-free selectivity to LOs and only less than 1% of aromatics. 407 Bao et al demonstrated that selective shielding of different types of MOR zeolite cages might vary the ethylene fraction in the products of syngas conversion. While the larger channel 12MR zeolites facilitate the formation of a broad range of hydrocarbons from methane to C 5+ , the smaller-sized ''side pockets'' 8MR counterparts selectively produce ethylene.…”

“…The first one implies variation of the distance between hydrogenation and acid sites by a different type of mechanical mixing. 388,391,407,409 Oxide and zeolite should be mixed, since their layer-by-layer packing facilitates methane production and RWGS (Fig. 28b).…”