nanomaterials Review A Review of Recent Advances of Dielectric Barrier Discharge Plasma in Catalysis Ju Li 1, Cunhua Ma 1,*, Shengjie Zhu 1, Feng Yu 1 , Bin Dai 1 and Dezheng Yang 2,3 1 Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan, School of Chemistry and Chemical Engineering, Shihezi University, Shihezi 832003, China; [email protected] (J.L.); [email protected] (S.Z.); [email protected] (F.Y.); [email protected] (B.D.) 2 Laboratory of Plasma Physical Chemistry, School of Physics, Dalian University of Technology, Dalian 116024, China; [email protected] 3 Key Laboratory of Ecophysics, College of Sciences, Shihezi University, Shihezi 832003, China * Correspondence: [email protected]; Tel.: +86-0993-205-8775 Received: 28 August 2019; Accepted: 21 September 2019; Published: 9 October 2019 Abstract: Dielectric barrier discharge plasma is one of the most popular methods to generate nanthermal plasma, which is made up of a host of high-energy electrons, free radicals, chemically active ions and excited species, so it has the property of being prone to chemical reactions. Due to these unique advantages, the plasma technology has been widely used in the catalytic fields. Compared with the conventional method, the heterogeneous catalyst prepared by plasma technology has good dispersion and smaller particle size, and its catalytic activity, selectivity and stability are significantly improved. In addition, the interaction between plasma and catalyst can achieve synergistic effects, so the catalytic effect is further improved. The review mainly introduces the characteristics of dielectric barrier discharge plasma, development trend and its recent advances in catalysis; then, we sum up the advantages of using plasma technology to prepare catalysts. At the same time, the synergistic effect of plasma technology combined with catalyst on methanation, CH4 reforming, NOx decomposition, H2O2 synthesis, Fischer–Tropsch synthesis, volatile organic compounds removal, catalytic sterilization, wastewater treatment and degradation of pesticide residues are discussed. Finally, the properties of plasma in catalytic reaction are summarized, and the application prospect of plasma in the future catalytic field is prospected. Keywords: dielectric barrier discharge plasma; heterogeneous catalyst; element doping; defect-rich; plasma catalysis 1. Introduction The plasma followed by solids, liquids and gases was later referred to as an ionized gas of the “fourth state of matter”. In 1928, Langmuir first proposed the term “plasma” [1]. Different from the properties of the three substances above, plasma is made up of a host of high-energy electrons, free radicals, chemically active ions and excited states. The total electric charge of electrons and various negative ions is roughly equal to that of positive ions, so it is generally electrically neutral. In effect, plasma has been found in several applications like materials science and microelectronics industries, and even in many emerging environments such as medical. Plasma is divided into low and high temperature plasma on the basis of the temperature of internal electrons. Based on thermodynamic equilibrium, the low temperature plasma can be further divided into thermal plasma and non-thermal plasma (NTP). Dielectric barrier discharge (DBD) is a non-thermal plasma. After the thermal plasma reaches a local equilibrium state, the electron temperature is nearly close to the overall gas temperature [2]. This group mainly contains various plasma torches. Nanomaterials 2019, 9, 1428; doi:10.3390/nano9101428 www.mdpi.com/journal/nanomaterials Nanomaterials 2019, 9, x FOR PEER REVIEW 2 of 33 Nanomaterials 2019, 9, 1428 2 of 34 Compared with other common gases, plasma has the following characteristics: as a collection of chargedCompared particles, with plasma other has common the conductivity gases, plasma similar has theto that following of metal characteristics: in which some as aions collection collide, of andcharged the movement particles, plasma of positive has the and conductivity negative charge similars generates to that of metalstrong in electric which someand magnetic ions collide, fields; and therefore,the movement it has of heat positive conduction and negative and chargesheat radiation. generates The strong total electric amount and of magnetic positive fields; and negative therefore, chargesit has heat in the conduction plasma is andalways heat equal. radiation. Any small The total space amount charge of density positive changes and negative will generate charges a huge in the electricplasma field is always intensity, equal. which Any will small restore space its chargeoriginal density state and changes maintain will its generate neutral astate. huge The electric chemical field characterintensity, is which lively, will and restore it is prone its original to chemical state reac andtions. maintain The itsplasma neutral processes state. The have chemical successfully character been is usedlively, in andthe ittwo is prone catalytic to chemical fields, namely reactions. catalyst The plasmapreparation processes and havedirect successfully excitation of been reactants used in [3]. the Catalyststwo catalytic play fields, a pivotal namely role catalyst in the preparationmodern industry. and direct Currently, excitation nearly of reactants all chemicals [3]. Catalysts in life play are a manufacturedpivotal role in through the modern catalytic industry. processes. Currently, However, nearly heterogeneous all chemicals in catalysis life are manufactured makes an important through impactcatalytic in processes.these catalytic However, processes heterogeneous [4]. catalysis makes an important impact in these catalytic processesDBD research [4]. has now been going on for more than a century. Siemens et al. [5] focused on the productionDBD researchof ozone, has and now the beenfirst experimental going on for morereport than was a made century. in 1857. Siemens The etdischarge al. [5] focused experiment on the deviceproduction they designed of ozone, has and many the first novel experimental features, one report of waswhich made is that in 1857.the electrode The discharge does not experiment contact withdevice the they plasma designed and is has located many outside novel features, the discha onerge of chamber. which isthat Therefore, the electrode DBD has does been not contactconsidered with tothe be plasma “ozone and discharge” is located for outside a long thetime. discharge Andrew chamber. and Tait Therefore,[6] called it DBD “silent has discharge” been considered due to to its be quiet“ozone and discharge” silent discharge for a long process time. in Andrew1860. Buss and [7] Tait made [6] a called significant it “silent contribution discharge” to duecharacterizing to its quiet theand discharge. silent discharge He discovered process that in 1860. air breakdown Buss [7] made between a significant parallel contributionelectrodes covered to characterizing by dielectrics the isdischarge. always accompanied He discovered by thatplenty air of breakdown tiny short-lived between current parallel wires. electrodes DBD is covered one type by dielectricsof the non- is thermalalways plasma accompanied (NTP), by which plenty can of substitute tiny short-lived the conventional current wires. catalytic DBD chemical is one type process of the that non-thermal operates underplasma high (NTP), temperature which can conditions substitute. Figure the conventional 1 represents catalytic two typical chemical DBD process electrode that devices, operates namely under planarhigh temperature and cylindrical conditions. DBD [8]. Figure The placement1 represents of two one typical or more DBD dielectric electrode layers devices, between namely the planarmetal electrodesand cylindrical is essential DBD [for8]. Thethe discharge placement operation. of one or moreTypical dielectric dielectric layers materials between are the glass, metal quartz electrodes and ceramic.is essential for the discharge operation. Typical dielectric materials are glass, quartz and ceramic. FigureFigure 1. 1. Two typicaltypical DBD DBD electrode electrode devices: devices: (a) planar(a) planar reactor; reactor; (b) cylindrical (b) cylindrical reactor; reactor; (c) two discharge(c) two dischargetypes of surfacetypes of discharge surface discharge and coplanar and discharge.coplanar discharge. Reproduced Reproduced with permission with permission from [8]; Copyrightfrom [8]; CopyrightElsevier, 2003. Elsevier, 2003. InIn a a DBD, DBD, the the average average temperature temperature of of high-energ high-energyy electrons electrons is is very very high, high, over over the the range range of of 10,000–100,00010,000–100,000 K, K, but but the the actual actual gas gas temperature temperature is is close close to to the the environment environment temperature. temperature. By By electron electron impactimpact ionization ionization and and excitation, excitation, source source gases gases can can produce produce active active radicals, radicals, ions, ions, excited excited atoms atoms and and molecularmolecular species species [9]. [9 ].The The cold cold plasma plasma characteristics characteristics of DBD, of DBD, as well as as well the asbombardment the bombardment of high- of energyhigh-energy electrons electrons and other and other reactive reactive ions ionsgenerated generated by gas by gasionization, ionization, can can ac achievehieve the the effects effects that that conventionalconventional means means cannot cannot achieve achieve