Various needle trap devices (NTDs) with different designs for different applications have been developed during the past decade. A theoretical model on the fundamentals of the NTD was recently proposed, which employed the theory of frontal (gas-solid) chromatography to describe the sampling process, where a gaseous sample was continuously introduced into the sorbent bed. In this investigation, different types of sorbent particles with different dimensions were packed into the needle as adsorbents. The effect of particle dimension, which would affect the packing density and consequently the capacity, the extraction efficiency, and desorption efficiency of the NTD were experimentally investigated and the proposed theory was validated. The results demonstrated that NTDs packed with small particles possess higher extraction capacity and efficiency but much higher resistance to flow as well. The higher resistance did not necessarily result in poor desorption efficiency, because desorption efficiency was affected by both the sorbent bed structure and the desorption gas flow. The relationships observed among those physical parameters provide valuable guidance on how to design an NTD with high performance potential for future applications. For particulate sampling, it was found that NTDs packed with different particles presented high collection efficiency of the particulates being investigated, and the collection efficiency was dominated by the pore size and distribution of the sorbent bed packed inside the needle. Collection efficiency also increased with increase in solidity of the sorbent bed; the increase in humidity of the aerosol sample; and the decrease of sampling rate. The results also provide valuable guidance on the optimisation of needle trap for particulate collection.

Various needle trap devices (NTDs) with different designs for different applications have been developed during the past decade. A theoretical model on the fundamentals of the NTD was recently proposed, which employed the theory of frontal (gas-solid) chromatography to describe the sampling process, where a gaseous sample was continuously introduced into the sorbent bed. In this investigation, different types of sorbent particles with different dimensions were packed into the needle as adsorbents. The effect of particle dimension, which would affect the packing density and consequently the capacity, the extraction efficiency, and desorption efficiency of the NTD were experimentally investigated and the proposed theory was validated. The results demonstrated that NTDs packed with small particles possess higher extraction capacity and efficiency but much higher resistance to flow as well. The higher resistance did not necessarily result in poor desorption efficiency, because desorption efficiency was affected by both the sorbent bed structure and the desorption gas flow. The relationships observed among those physical parameters provide valuable guidance on how to design an NTD with high performance potential for future applications. For particulate sampling, it was found that NTDs packed with different particles presented high collection efficiency of the particulates being investigated, and the collection efficiency was dominated by the pore size and distribution of the sorbent bed packed inside the needle. Collection efficiency also increased with increase in solidity of the sorbent bed; the increase in humidity of the aerosol sample; and the decrease of sampling rate. The results also provide valuable guidance on the optimisation of needle trap for particulate collection.

The direct hydrogenation of CO2 to methanol is an attractive approach to employ the greenhouse gas as a chemical feedstock. However, the commercial copper catalyst, used for methanol synthesis from CO-rich syngas, suffers from deactivation at elevated CO2 partial pressure. An emerging alternative is represented by In2O3 as it withstands the hydrothermal conditions induced by the reverse water-gas shift reaction. The active sites for the adsorption of CO2 and the subsequent conversion into methanol were shown to be oxygen vacancies on the surface of In2O3. In this study, N2O was utilized as a probe molecule to quantify the number of vacancies on indium oxide catalysts. The number of inserted oxygen atoms could be correlated to the respective CO2 hydrogenation activity. Furthermore, the atomic efficiency of indium was enhanced by applying atomic layer deposition of indium oxide on ZrO2.