Catalytic behavior of alkali-treated Pt/HMOR in n-hexane hydroisomerization

Abstract

Bifunctional Pt-HMOR catalysts were prepared by incipient wetness impregnation of various desilicated MOR obtained by alkaline treatment using NaOH concentrations ranging from 0.1 to 0.5 M. The zeolite structural changes upon modification were investigated by several techniques including powder X-ray diffraction, 27 Al and 29 Si MAS-NMR spectroscopy, N 2 adsorption, pyridine adsorption followed by infrared spectroscopy and the catalytic model reaction of m-2 xylene transformation. For low alkaline concentration the zeolite acidity is preserved, along with a slight increase of the volume correspondent to the larger micropores due to the removal of extra-framework debris already existent at the parent zeolite At higher NaOH concentrations there is a significant loss of crystalinity and acidity as well as the formation of mesoporosity. The characterization of the metal function show similar patterns for Pt-HMOR and Pt-M/0.1 samples, with Pt particles located mainly inside the inner porosity. In contrast, large Pt particles become visible at the intercrystalline mesoporosity of MOR crystals developed during the desilication treatments at severe alkaline conditions. The catalytic results obtained for n-hexane hydroisomerization showed an improved selectivity for dibranched over monobranched isomers for Pt-M/0.1 sample, likely due to the preservation of the support acidity and the slight enlargement of the micropores. This work is a new example in which the mesoporous development does not improve the catalytic efficiency of the zeolites, whereas mild alkaline desilication might be considered as an effective solution to produce customized catalysts with enhanced performance for a given application.

Mordenite Nanorods Prepared by an Inexpensive Pyrrolidine‐based Mesoporogen for Alkane Hydroisomerization

“…The introduction of a second level of intracrystalline porosity to the MOR pore system would be advantageous to the many acid‐catalyzed hydrocarbon conversion reactions that involve large paraffinic and aromatic molecules. A general “top‐down” approach to prepare mesoporous mordenite zeolites via desilication, dealumination or a combination of these approaches has been extensively examined. Even though these techniques are commercially available and can be scaled up, there is little control over the textural and acidic properties of the final materials.…”

Catalytic Behavior of Alkali Treated H-MOR in Selective Synthesis of Ethylenediamine via Condensation Amination of Monoethanolamine

“…When NaOH concentration was 0.1 mol/L, the RC of the sample reached its highest value (115%). This is because the amorphous aluminosilicate or zeolites can be removed by the NaOH solution [18] and re-insertion of the aluminum species into the zeolite framework can occur during alkali treatment [20]. However, alkali treatment under certain harsh conditions can extract a large number of Si atoms from the framework to produce mesopores The X-ray diffraction (XRD) patterns ( Figure 3) show that all the samples before and after alkali treatment present the same diffraction peaks as those of the parent H-MOR (9.7, 19.7, 22.4, 25.8, and 26.4 • of 2θ).…”

“…Alternatively, EDA can be produced via reductive amination of monoethanolamine (MEA) with hydrogen and ammonia over nickel or cobalt catalysts [3]. However, a higher reaction pressure (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) of hydrogen is an essential prerequisite to achieve satisfactory catalytic performance in the above process [1,4], which makes this manufacturing process potentially dangerous for use in industry.…”

Hydroisomerization of Renewable and Fossil n‐Alkanes over Bifunctional Dealuminated ZSM‐5 Catalysts

“…Mesopores can also be introduced intentionally into the zeolite by desilication with alkaline solutions. The resulting hierarchical pore system improves the shape-selective properties of the catalysts towards the formation of bulkier multi-branched isomers [11,[18][19][20][21][22].…”