مقاله انگلیسی رایگان در مورد اثر نقایص کربن بر عملکرد کاتالیزوری کربن نیتروژن – الزویر 2018

The carbon defects in nitrogen-doped carbon were controlled by removing the N atoms under different temperatures during the catalyst preparation process. The synthesised catalysts were characterised by multiple techniques, and the catalytic performance was evaluated under experimental conditions of gas hourly space velocity (C2H2) = 36 h−1 at 220 °C. The catalytic performance of the synthesised nitrogen-doped carbon for acetylene hydrochlorination increased with the increment of carbon defect. Carbon defects in the catalysts were proposed to affect the adsorption of C2H2 and HCl and promote their conversion. The regeneration of the nitrogen-doped carbon catalyst was found to be effective by using high-temperature treatment in an NH3 atmosphere.

Introduction

Acetylene hydrochlorination is a very important method for manufacturing vinyl chloride monomer (VCM) in China because China contains rich deposits of coal but lacks oil. However, the industrial catalyst for acetylene hydrochlorination is HgCl2, which is toxic to the human body and the environment [1]. Therefore, the exploitation of environmentally friendly non-mercury catalysts is attracting increasing attention for acetylene hydrochlorination. In the past decades, Au catalysts have been found to be effective for acetylene hydrochlorination. In our previous work, we designed an Au catalyst whose acetylene conversion rate reached 100%. This catalyst could be stably used for 6513 h under industrial application conditions [2,3]. Wei et al. [4] found that a Au catalyst with thiocyanate ligands could operate for over 3000 h in a 4 t per annum scale pilot experiment. Hutchings et al. [5] reported very exciting results for the development of non-mercury acetylene hydrochlorination catalysts. By using thio ligands as soft donor atoms, active Au+ and Au° were present consistent with the formation and deposition of Au catalyst, and the synthesised catalyst could last over 3000 kg VCM/kg catalyst, which is a very low Au loading. These investigations greatly accelerated the commercialisation of non-mercury catalysts for acetylene hydrochlorination. However, given the high cost and scarcity of Au, low-cost catalysts are being sought as non-mercury replacement catalysts for acetylene hydrochlorination. In our previous work, we synthesised C3N4 for acetylene hydrochlorination, and we found that the acetylene conversion rate of this catalyst can reach 75% of the HgCl2 catalyst efficiency. According to density functional theory (DFT) calculations, carbon atoms were the adsorption sites for acetylene, and nitrogen atoms were the adsorption sites for hydrogen chloride [6]. The reaction activation energy was 77.94 kcal/mol, which is much higher than AuCl3 (11.9 kcal/mol) [7]. Thereafter, many groups have synthesised catalysts with nitrogendoped carbons that display excellent catalytic performance. Wei et al [8]. reported nitrogen-doped carbon nanotubes that could greatly enhance the adsorption of acetylene. This catalyst showed excellent catalytic properties with turn over frequency (TOF) of up to 2.3 × 10−3 /s. Pan et al. [9] found that the catalyst activity increased with increasing N content, and only carbon atoms linked to pyrrolic nitrogen could adsorb acetylene. Thus, they found that the type of nitrogen played a major role in this reaction. The catalyst performance stabilised at above 80% under 30/h (C2H2) and 200 °C during 150 h. In our previous work, we considered the effect of the nitrogen species in the nitrogen-doped catalyst for acetylene hydrochlorination and found that the effectiveness of the nitrogen species for acetylene hydrochlorination followed this order: pyrrolic N > graphitic N > pyridinic N [10]. On the basis of that sequence, we then designed and synthesised boron and nitrogen dual-doped graphene (B, N-G) materials. The acetylene conversion on that catalyst could reach to 95%, which was very close to the performance of Au and Hg catalysts [11].