Dual Effects of Zinc Species on Active Sites in Bifunctional Composite Catalysts Zr/H[Zn]ZSM-5 for Alkylation of Benzene with Syngas

Abstract

Bifunctional composite catalysts Zr/H­[Zn] x Z with different Zn contents were prepared by combining the impregnation and physical mixing method. The effect of zinc species on two active sites in bifunctional composite catalysts Zr/H­[Zn]­ZSM-5 for alkylation of benzene with syngas has been investigated. The results indicated that the introduction of Zn greatly improves the catalytic performance and the selectivity of target products and changed with the change of Zn content. The sample Zr/H­[Zn]3Z exhibited the highest total selectivity of toluene and xylene of 91% and the benzene conversion of 18% at 400 °C under 3.3 MPa; nevertheless, the sample Zr/H­[Zn]5Z showed the highest benzene conversion and xylene selectivity, which reached 31 and 27%, respectively. The acidic properties and state of Zn species of H­[Zn] x Z zeolites have also been explored. All evidence suggested that most of Zn introduced into HZ zeolite existed in the catalyst as Zn­(OH)+, forming new Zn-Lewis acid at the expense of Brønsted acid. The Zn species plays a role in three aspects in the alkylation reaction between benzene and syngas. First, the Zn species can provide H species for ZrO2 activation of CO by promoting H2 activation, thus generating more methanol; second, Zn­(OH)+ species formed in zeolite can inhibit the side reactions of methanol so as to promote the alkylation of benzene and methanol; finally, the Zn-Lewis acidic sites can inhibit the cracking reaction of C6+ olefins and further promote the dehydrogenation aromatization reaction.

One-Pass Conversion of Benzene and Syngas to Alkylbenzenes by Cu–ZnO–Al2O3 and ZSM-5 Relay

“…4 to differentiate situation of Lewis and Brønsted acid sites of ZSM-5. The peaks at 1450 and 1545 cm −1 correspond to Lewis acid sites and Brønsted acid sites of ZSM-5, respectively [ 20 , 31 , 32 ]. Brønsted acids mainly come from the -OH group on the framework of ZSM-5 where the Si is replaced by Al, resulting in an imbalance of charge and then -OH produced by adsorption of proton, while Lewis acid mainly originates from the coordinated unsaturated Al 3+ [ 33 – 35 ].…”

“…There is a temperature matching relationship between the two components in the Cu–ZnO–Al 2 O 3 /ZSM-5(31) dual-function catalyst [ 20 , 49 ]. Generally, the temperature of Cu–ZnO–Al 2 O 3 catalyzed synthesis of methanol at 230–280 °C [ 50 – 52 ], while the HZSM-5 catalyzed benzene and methanol alkylation needs to be higher than 400 °C [ 20 , 49 ].…”

“…There is a temperature matching relationship between the two components in the Cu–ZnO–Al 2 O 3 /ZSM-5(31) dual-function catalyst [ 20 , 49 ]. Generally, the temperature of Cu–ZnO–Al 2 O 3 catalyzed synthesis of methanol at 230–280 °C [ 50 – 52 ], while the HZSM-5 catalyzed benzene and methanol alkylation needs to be higher than 400 °C [ 20 , 49 ]. In the Cu–ZnO–Al 2 O 3 /ZSM-5(31) catalyzed alkylation reaction of benzene and syngas, when the temperature is lower than 400 °C, although it is beneficial to the production of intermediate methanol from syngas on Cu–ZnO–Al 2 O 3 , the ability of ZSM-5 to activate benzene is limited due to the low reaction temperature.…”

The dependence of high catalytic performance on the tunable oxygen vacancy in the CZxS/Zn‐HZSM‐5 bifunctional catalyst for alkylation of benzene and syngas

“…The existence of the mesoporous was an important reason for the large specific area of CZ x S samples. [10,19,27,28] Table 1 showed the specific surface area and pore volume of each sample calculated based on the N 2 adsorption and desorption isotherms. As illustrated in Table 1, the specific surface area of CZ x S significantly increased when Zr was inserted into CeO 2 and reached maximum for a Zr/Ce ratio of 4, and then decreased for a higher Zr/Ce ratio.…”

“…[1,5] The production of toluene/xylene by alkylated benzene with methanol has received much attention, [6,7] in which methanol can be synthesized separately from syngas that can be got from abundant resources, for example, coal, biomass, natural gas or organic waste. [8][9][10][11][12][13] As a result, an in situ benzene methylation process with syngas is expected to both meet the growing demand for toluene/xylene and take full advantage of syngas. [3] The major challenge in benzene alkylated with syngas is to find a high-efficient catalyst that can perform both catalytic hydrogenation and alkylation activity, allowing syngas to be converted into methanol and then methanol to be alkylated with benzene.…”