Catalytic Pyrolysis of Methane to Hydrogen over Carbon (from cellulose biochar) Encapsulated Iron Nanoparticles,Energy & Fuels

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Catalytic Pyrolysis of Methane to Hydrogen over Carbon (from cellulose biochar) Encapsulated Iron Nanoparticles
Energy & Fuels ( IF 5.2 ) Pub Date : 2021-08-04 , DOI: 10.1021/acs.energyfuels.1c01620
Rahul Kundu ₁ , Vaidheeshwar Ramasubramanian ₁ , Sai Teja Neeli ₁ , Hema Ramsurn ₁

Affiliation

The catalytic performance of carbon encapsulated iron nanoparticles (CEINPs) for methane decomposition was investigated over a range of temperatures between 700 and 800 °C with varying iron concentrations (20, 30, and 40 wt %) in a semicontinuous flow fixed bed reactor. CEINPs were prepared by impregnating a cellulose biochar support (carbon source) with iron nitrate solution. This mixture was dried at 110 °C for 72 h in air followed by pyrolysis at 1000 °C in a N₂ atmosphere. Unlike conventional iron-based catalysts, in CEINPs, the iron nanoparticles were encapsulated in a graphitic shell that prevented atmospheric oxidation and sintering at high temperature, improving the thermal stability of the catalysts. The fresh CEINPs did not contain any metal oxides and had only the following phases: elemental iron, iron carbides, activated carbon, and graphitic carbon, which allowed for the catalyst reduction step (in H₂) to be eliminated. The decomposition of methane being an endothermic reaction showed better catalytic activity with an increase in temperature with the highest conversion of 95.7% observed at 800 °C. There are four different active sites in the catalyst, namely, graphite, graphite encapsulated iron nanoparticles, uncovered iron nanoparticles, and activated carbon. In the case of 20 wt % CEINP, the presence of higher amounts of activated carbon and graphite with a lower amount of Fe negatively impacted methane decomposition, confirming the importance of Fe as an active site. At 800 °C, the maximum catalytic performance was exhibited by 30 wt % CEINP where the initial methane conversion was 95.7% and dropped to 36.8% after 180 min of reaction. The higher conversion was due to the combined optimum amounts of Fe, graphite, and activated carbon active sites. In the case of 40 wt % CEINP, the higher amount of Fe resulted in the agglomeration of Fe nanoparticles and reduction in surface area, leading to lower methane conversions. The surface area of the spent catalysts reduced appreciably in all cases due to carbon deposition from CH₄ in the form of coke and graphite (on non-encapsulated Fe nanoparticles), resulting in catalyst deactivation.

中文翻译：

在碳（来自纤维素生物炭）包封的铁纳米颗粒上催化热解甲烷到氢气

在半连续流动固定床反应器中，在 700 至 800 °C 的温度范围内，以不同的铁浓度（20、30 和 40 重量%）研究了碳包封的铁纳米粒子（CEINP）对甲烷分解的催化性能。CEINPs 是通过用硝酸铁溶液浸渍纤维素生物炭载体（碳源）来制备的。该混合物在空气中在 110°C 下干燥 72 小时，然后在 N _{2 中}在 1000°C 下热解气氛。与传统的铁基催化剂不同，在 CEINP 中，铁纳米颗粒被包裹在石墨壳中，防止大气氧化和高温烧结，提高了催化剂的热稳定性。新鲜的 CEINP 不含任何金属氧化物，只有以下相：元素铁、碳化铁、活性炭和石墨碳，它们允许催化剂还原步骤（在 H ₂) 被淘汰。作为吸热反应的甲烷分解显示出更好的催化活性，随着温度的升高，在 800°C 下观察到的最高转化率为 95.7%。催化剂中有四种不同的活性位点，即石墨、石墨包裹的铁纳米颗粒、未覆盖的铁纳米颗粒和活性炭。在 20 wt % CEINP 的情况下，较高量的活性炭和石墨以及较低量的 Fe 的存在对甲烷分解产生负面影响，证实了 Fe 作为活性位点的重要性。在 800 °C 时，30 wt% CEINP 表现出最大的催化性能，其中初始甲烷转化率为 95.7%，反应 180 分钟后降至 36.8%。较高的转化率是由于 Fe、石墨、和活性炭活性位点。在 40 wt % CEINP 的情况下，较高量的 Fe 导致 Fe 纳米颗粒的团聚和表面积减少，从而导致甲烷转化率降低。由于 CH 的碳沉积，废催化剂的表面积在所有情况下都明显减少₄以焦炭和石墨的形式（在非包封的 Fe 纳米粒子上），导致催化剂失活。

更新日期：2021-08-19

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