Synergetic effect of Mn, Ce, Ba, and B modification and moderate desilication of nanostructured HZSM-5 catalyst on conversion of methanol to propylene

Abstract

Modified mesoporous HZSM-5 catalysts were prepared by controlled desilication using a mixture of NaOH and TPAOH (tetrapropylammonium hydroxide) and impregnation of metals (Mn, Ce, and Ba) and metalloid B. The catalytic performances of all prepared catalysts for methanol to propylene (MTP) reaction were evaluated in a fixed bed reactor under atmospheric pressure at 480°C. The parent and modified catalysts were characterized by XRD, ICP-OES, FE-SEM, NH 3-TPD, FT-IR, BET, and TGA techniques. The catalyst loaded with 2 wt.% manganese on desilicated HZSM-5 demonstrated the best catalytic performance in terms of the highest selectivity of C = 2 to C = 4 olefins (about 93%) and about 52% selectivity of propylene at near 99% methanol conversion in the MTP reaction for a long operation (264 h). The improved catalytic performance can be attributed to the high surface area and the formation of mesopores on the zeolite crystals in conjunction with the appropriate acidity.

Integrated Experimental and Modeling Approach for Methanol-to-Propylene Conversion over Mn-Modified Desilicated HZSM-5 Catalyst in a Fluidized Bed Reactor

“…The literature survey revealed that the olefin-based cycle was dominated for HZSM-5 catalyst and that the ethylene production via methylation/dealkylation of aromatic intermediates could be ignored. , In addition, according to our previous study, the synergetic modification by Mn impregnation and moderate desilication reduced both the density and strength of the strong acid sites. Since the low amount of total acid sites (especially the amount and strength of strong acid sites) inhibits the undesirable reaction of aromatization, cyclization, and hydrogen transfer, ,− the formation of aromatic intermediates (in the aromatic-based cycle) from heavy olefins (included in the C 5 + lump) in the olefin-based cycle are reduced and, consequently, the aromatic-based cycle is limited.…”

“…The Mn-modified desilicated HZSM-5 catalyst (denoted as Mn–DZSM-5) was synthesized according to the procedure reported in our previous paper . Briefly, first the high silica Na–ZSM-5 catalyst was hydrothermally prepared with a gel molar composition of 20 SiO 2 :0.05 Al 2 O 3 :1 TPAOH:1.5 Na 2 O:200 H 2 O .…”

“…The physicochemical properties of the Mn–DZSM-5 catalyst are listed in Table S1. A detailed description of the preparation procedure and the characterization of the Mn–DZSM-5 catalyst has been reported elsewhere . The catalyst was pressed, crushed, and then sieved by 35–40 mesh particles (about 450 μm) for catalytic tests.…”

“…Various methods have been reported in the literature to improve the catalytic activity and performance of HZSM-5, comprising generation of mesoporosity in microporous HZSM-5 − (to overcome diffusion limitation and postpone the catalyst deactivation via desilication) and alteration in zeolite acidity − (to increase propylene selectivity via doping with some metals). Our former study showed that the synergetic modification by controlled desilication and Mn impregnation over high-silica HZSM-5 catalyst plays a positive role in propylene selectivity and catalyst activity …”

Kinetic Perspective on Methanol to Propylene Process via HZSM-5 Catalyst: Balancing between Reaction and Diffusion

“…Several MTP process technologies were developed over the past decades such as fixed bed, fluidized bed, and moving bed related MTP processes. Fixed bed MTP technology has been studied and developed in various studies involving the use of HZSM-5 based catalysts such as Me-ZSM-5; PbO/HZSM-5; Mn, Ce, Ba, or B/HZSM-5; HZSM-5/cordierite monolith; HZSM-5; , and HZSM-5/SiC . Fixed bed technology is well-known for its reduced back-mixing feature to produce desired plug flow behavior for maximized propylene selectivity.…”