Contents lists available at ScienceDirectApplied Surface Sciencejournal homepage: www.elsevier.com/locate/apsuscFull length articleThe negative ef f ect of P addition of La/HZSM-5 on the catalytic performancein methyl mercaptan abatementXiaohua Cao a , Dedong He b , Jichang Lu a , Yutong Zhao a , Yi Mei b , Caiyun Han a, ? , Yongming Luo a, ?a Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650500, PR Chinab Faculty of Chemical Engineering, Kunming University of Science and Technology, Kunming 650500, PR ChinaA R T I C L E I N F OKeywords:La/HZSM-5P modif i cationNegative ef f ectSurface active oxygenBasic-acid centersCH 3 SH decompositionA B S T R A C TThe ef f ect of P addition on the catalytic performance of La/HZSM-5 in methyl mercaptan abatement was in-vestigated in the present work. It was shown that the addition of phosphorus could decrease the amounts ofstrong acid sites over the P-doped 13%La/HZSM-5 samples, but expected coke resistance ability was not ob-tained. To our surprise, P-doped 13%La/HZSM-5 samples exhibited decreased activity and stability for methylmercaptan abatement. Moreover, the 13%La/HZSM-5 supported P catalysts were prepared and characterized byNH 3 -TPD, FT-IR, XRD and XPS, and it was found that the introduction of P species into La/HZSM-5 catalystprovokes a reaction with La 2 O 3 and La 2 O x (CO 3 ) y species, which were reported to be active sites for methylmercaptan conversion. As a result, P addition generated some inactive species such as AlPO 4 , Al(PO 3 ) 3 , LaPO 4and La(PO 3 ) 3 species, causing the deactivation of the catalyst. These results conversely proved the necessarypresence of active La 2 O 3 and La 2 O x (CO 3 ) y species in the La/HZSM-5 catalyst for eliminating CH 3 SH.1. IntroductionVolatile organic compounds (VOCs) are generally regarded to causeserious air pollution, such as photochemical smog and urban haze[1–3]. Methyl mercaptan (CH 3 SH) is a sulfur-containing VOC, whichhas extremely low odor threshold and wide range of sources [4,5]. Atthe same time, its toxic ef f ect on human health cannot be ignored, sincevery small amount of CH 3 SH can cause headache, nausea and an-esthesia to the human beings, while high concentration of CH 3 SH canlead to respiratory paralysis and death [6]. Furthermore, due to its highacidity, the presence of CH 3 SH can give corrosion to reactors and pi-pelines, and poison catalyst from many industry processes [7]. There-fore, the abatement of this sulfur-containing VOC (CH 3 SH) is of im-portance.As a matter of fact, various methods for the removal of CH 3 SH havebeen recently reported [8–11]. Among them, catalytic decompositionmethod has attracted a wide spread attention, because it is easy tooperate with no need for additional additives [10,11]. Besides, the f i nalsulfur-containing product (H 2 S) can be commercially devoted to pro-duce elemental sulfur in the Claus process [12]. Throughout the recentresearch, HZSM-5 zeolite [13–15], rare-earth (e.g. Nd, Er, Y, Sm, La, Ceand Pr) modif i ed HZSM-5 zeolite [16–19], cerium-based oxide [20–23],Cr-based catalyst [24,25] has been investigated to improve the catalyticperformance for CH 3 SH abatement. However, it is not hard to f i nd thatvarious catalysts have dif f erent active sites for CH 3 SH elimination, butthe identif i cation of its active phase has not been clearly presented. Infact, HZSM-5 zeolite can break the CeS bond and CeH bond under theaction of the strong Brønsted acid sites. Nevertheless, the correspondingtemperature for the complete conversion of CH 3 SH over pure HZSM-5was as high as 600 °C [11]. Compared to HZSM-5, cerium-based oxidecatalyst can provide a lot of basic centers as well as active sites [20],which can decrease the reaction temperature from 600 °C (HZSM-5catalyst) to 450°C via oxygen and sulfur exchange mechanism. He et al.found that the reaction temperature for catalytic decomposing ofCH 3 SH over Cr-based catalyst decreased to 400°C, and the deactivationof the Cr-based catalyst was caused by the process that the generatedactive oxygen species were consumed and f i nally became Cr 2 S 3 speciesduring the reaction [24]. Surprisingly, the latest reported La/HZSM-5sample can not only provide suf f i cient basic sites for eliminating cokedeposit, but also showed decreased activation temperature for theconversion of CH 3 SH, since the strong acid sites over the HZSM-5 wereweaken [19]. All these studies demonstrated that increasing the basiccenters can decrease the activation temperature. It was discovered fromthe literatures that phosphorus species (P), acted as typical basic group,have ability to decrease the acidity of the zeolite catalysts. As reportedpreviously, modif i cation of HZSM-5 zeolite with phosphorus (basicpromoter) has been widely tested in dif f erent reactions, such as cata-lytic cracking of C 4 -olef i n to generate propylene [26,27]，methanol-to-https://doi.org/10.1016/j.apsusc.2019.07.264Received 13 March 2019; Received in revised form 24 July 2019; Accepted 29 July 2019? Corresponding authors.E-mail addresses: shenxifu@sina.com (C. Han), environcatalysis222@yahoo.com (Y. Luo).Applied Surface Science 494 (2019) 1083–1090Available online 30 July 20190169-4332/ © 2019 Elsevier B.V. All rights reserved.T
